Isolate fixtures and resolver cache

[Vladyslav-Kuksiuk]

This PR:

• Makes source resolver cache state explicit per processing operation.
• Moves embedding tests to per-test temp documentation fixtures.
• Cleans up related Go doc comments and redundant processor state handling.

Resolves this issue.

[Copilot]

Pull request overview

This PR addresses issue #61 by removing shared mutable state from embedding/fragmentation processing and tests, enabling the Go test suite to run safely with default package parallelism (no CI -p 1).

Changes:

• Introduces a per-processing-operation fragmentation.Resolver that owns the source-fragment cache, and threads it through embedding/parsing.
• Updates embedding tests to use per-test temp documentation roots and copies fixtures into them instead of writing into a shared directory.
• Removes cache reset logic and updates CI to run go test without -p 1.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
fragmentation/resolver.go	Replaces the process-global resolver cache with a per-instance Resolver and method-based APIs.
fragmentation/cache.go	Removes the cache clear() API now that caches are per operation/instance.
fragmentation/fragmentation_test.go	Updates tests to create a resolver per spec and adds coverage for cache isolation between resolvers.
embedding/processor.go	Stores a resolver in Processor and passes it into parsing context creation.
embedding/parsing/instruction.go	Uses a resolver for content/reference resolution and adds fallback behavior.
embedding/parsing/context.go	Adds resolver ownership to parsing Context and injects it into instructions.
embedding/orchestration.go	Shares a resolver across processors within a single orchestration run.
embedding/embedding_test.go	Uses per-test temp dirs and os.CopyFS to isolate writable doc fixtures.
.github/workflows/check.yml	Removes -p 1 from unit and showcase test runs.

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[Oleg-Melnik]

@Vladyslav-Kuksiuk LGTM with Copilot’s comments addressed before merging.