Fix Python namespace normalization during refinement

[AayushP123]

Summary

Normalizes Python CodeDOM namespace segments to snake_case during language refinement. Normalizes the configured client namespace before path and import writers calculate namespace differentials. Updates public API export expectations and adds coverage for root traversal and configured namespace casing.

Validation

dotnet test tests/Kiota.Builder.Tests/Kiota.Builder.Tests.csproj --no-restore --nologo --filter 'FullyQualifiedName!~KiotaSearcherTests' --verbosity quiet (2,185 passed, 2 skipped)

Focused Python namespace, writer, export, and builder tests: 41 passed.

Fixes #7715

[Copilot]

Pull request overview

This pull request fixes Python namespace normalization at the CodeDOM refinement stage by ensuring namespace segments are converted to snake_case during refinement (including proper traversal from the root namespace) and by normalizing the configured client namespace prefix before Python path/import logic computes namespace differentials.

Changes:

• Normalize Python CodeNamespace.Name segments to snake_case during PythonRefiner.RefineAsync, ensuring traversal starts from the root namespace.
• Normalize clientNamespaceName to snake_case inside PythonWriter before initializing the path segmenter and namespace-dependent writers.
• Update and extend tests to validate refined namespace casing, writer prefix normalization behavior, and public API export expectations.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Kiota.Builder/Refiners/PythonRefiner.cs	Adds a refinement pass to snake_case namespace segments and ensures traversal runs from the root namespace.
src/Kiota.Builder/Writers/Python/PythonWriter.cs	Normalizes the configured client namespace prefix to snake_case before path/import computations.
tests/Kiota.Builder.Tests/Refiners/PythonLanguageRefinerTests.cs	Adds coverage asserting namespace segment snake_casing and namespace lookup consistency post-refinement.
tests/Kiota.Builder.Tests/Writers/Python/PythonWriterTests.cs	Adds coverage ensuring client namespace prefix normalization affects path segmentation as expected.
tests/Kiota.Builder.Tests/Export/PublicAPIExportServiceTests.cs	Updates expected Python export namespace strings to reflect refined snake_case namespace names.
tests/Kiota.Builder.Tests/KiotaBuilderTests.cs	Updates a namespace lookup expectation for Python to match snake_cased namespaces after refinement.