convert unreleased sections in changelogs to towncrier

[lmolkova]

• Fragments use towncrier orphan naming (+<slug>.<type>) — these entries reference old opentelemetry-python-contrib PRs, so the auto-appended genai-repo link would be wrong. Orphans disable that link; the original contrib PR link is kept inline in the body.
• Small changelog_template.j2 tweak so orphan fragments don't render a stray () (no-op for normal numbered fragments).

[Copilot]

Pull request overview

Migrates legacy static “## Unreleased” sections in package CHANGELOG.md files into Towncrier fragment files (using orphan-style fragment names to avoid auto-linking to this repo’s PRs), and adjusts the shared Towncrier Jinja template to avoid rendering empty () when a fragment has no issue/PR link.

Changes:

• Removed static ## Unreleased sections (and related explanatory text) from multiple package changelogs.
• Added Towncrier fragments representing the previously-unreleased entries (using +<slug>.<type> orphan naming).
• Updated scripts/changelog_template.j2 to only render (<links>) when the fragment has link values.

Reviewed changes

Copilot reviewed 33 out of 33 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
util/opentelemetry-util-genai/CHANGELOG.md	Removes the legacy static “Unreleased” section so releases are fully Towncrier-driven.
util/opentelemetry-util-genai/.changelog/+stream-wrapper-base-classes.added	Towncrier fragment for stream wrapper base classes entry.
util/opentelemetry-util-genai/.changelog/+sampling-attributes-on-start.changed	Towncrier fragment for sampler-attributes-on-start entry.
util/opentelemetry-util-genai/.changelog/+sampling-attribute-on-instantiation.changed	Towncrier fragment for sampling attribute application entry.
util/opentelemetry-util-genai/.changelog/+inference-invocation-base-params.changed	Towncrier fragment for inference invocation params change entry.
util/opentelemetry-util-genai/.changelog/+google-genai-migration-prep.changed	Towncrier fragment for google-genai migration prep entry.
scripts/changelog_template.j2	Prevents stray () for fragments that produce no issue/PR link values.
instrumentation/opentelemetry-instrumentation-google-genai/CHANGELOG.md	Removes static “Unreleased” section in favor of Towncrier fragments.
instrumentation/opentelemetry-instrumentation-google-genai/.changelog/+reasoning-output-tokens-attr.added	Towncrier fragment for reasoning output tokens attribute entry.
instrumentation/opentelemetry-instrumentation-google-genai/.changelog/+cache-read-input-tokens-attr.added	Towncrier fragment for cache-read input tokens attribute entry.
instrumentation/opentelemetry-instrumentation-genai-weaviate-client/CHANGELOG.md	Removes legacy static “Unreleased” section scaffolding, leaving Towncrier start marker.
instrumentation/opentelemetry-instrumentation-genai-openai/CHANGELOG.md	Removes static “Unreleased” section in favor of Towncrier fragments.
instrumentation/opentelemetry-instrumentation-genai-openai/.changelog/+tool-definitions-span-attr.added	Towncrier fragment for tool definitions span attribute entry.
instrumentation/opentelemetry-instrumentation-genai-openai/.changelog/+refactor-stream-wrappers.changed	Towncrier fragment for stream wrapper refactor entry.
instrumentation/opentelemetry-instrumentation-genai-openai-agents/CHANGELOG.md	Removes static “Unreleased” section in favor of Towncrier fragments.
instrumentation/opentelemetry-instrumentation-genai-openai-agents/.changelog/+populate-instructions-tool-definitions.added	Towncrier fragment for populating instructions/tool definitions entry.
instrumentation/opentelemetry-instrumentation-genai-openai-agents/.changelog/+package-metadata-readme.added	Towncrier fragment for package metadata/README documentation entry.
instrumentation/opentelemetry-instrumentation-genai-openai-agents/.changelog/+align-agentspandata-stubs.changed	Towncrier fragment for AgentSpanData stub alignment entry.
instrumentation/opentelemetry-instrumentation-genai-langchain/CHANGELOG.md	Removes static “Unreleased” section in favor of Towncrier fragments.
instrumentation/opentelemetry-instrumentation-genai-langchain/.changelog/+wrapt-2-compat.fixed	Towncrier fragment for wrapt 2.x compatibility fix entry.
instrumentation/opentelemetry-instrumentation-genai-langchain/.changelog/+llm-invocation-span-support.added	Towncrier fragment for LLM invocation span support entry.
instrumentation/opentelemetry-instrumentation-genai-langchain/.changelog/+genai-utils-handler.added	Towncrier fragment for genai utils handler support entry.
instrumentation/opentelemetry-instrumentation-genai-langchain/.changelog/+log-metrics-provider.added	Towncrier fragment for log/metrics provider addition entry.
instrumentation/opentelemetry-instrumentation-genai-claude-agent-sdk/CHANGELOG.md	Removes static “Unreleased” section in favor of Towncrier fragments.
instrumentation/opentelemetry-instrumentation-genai-claude-agent-sdk/.changelog/+util-genai-dependency-range.changed	Towncrier fragment for util-genai dependency range change entry.
instrumentation/opentelemetry-instrumentation-genai-anthropic/CHANGELOG.md	Removes static “Unreleased” section (including “Added” subsection) in favor of Towncrier fragments.
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+util-genai-dependency-range.changed	Towncrier fragment for util-genai dependency range change entry.
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+wrapt-2-compat.fixed	Towncrier fragment for wrapt 2.x compatibility fix entry.
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+messages-stream-helper.added	Towncrier fragment for Messages.stream() helper instrumentation entry.
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+async-stream-wrappers.added	Towncrier fragment for async stream wrappers entry (multi-line).
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+sync-streaming-support.added	Towncrier fragment for sync streaming support entry (multi-line).
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+initial-implementation.added	Towncrier fragment for initial implementation entry.
instrumentation/opentelemetry-instrumentation-genai-anthropic/.changelog/+sync-messages-create.added	Towncrier fragment for sync Messages.create instrumentation entry (multi-line).