Fix parenthesized PEP 508 requirements

[andrew]

Fixes #52.

Strip optional parentheses around PEP 508 version constraints without changing extras or environment marker handling.

Add regression fixtures covering the affected Poetry requirements.

[Copilot]

Pull request overview

Fixes parsing of PEP 508 dependency strings that wrap the version specifier in optional parentheses (e.g., requests (>=2.26,<3.0)), ensuring the package name and version constraint are extracted correctly and PURLs are generated without spurious ( / ) characters.

Changes:

• Update parsePEP508 to strip a trailing ( from the extracted name and a trailing ) from the extracted version constraint when the requirement uses parenthesized constraints.
• Add unit tests for parsePEP508 covering parenthesized constraints (including extras and environment markers).
• Add a regression fixture pyproject.toml plus an integration-level test asserting correct dependency Name, Version, and PURL output from Parse.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
testdata/pypi/pep508-parenthesized/pyproject.toml	Adds a PEP 621 dependencies fixture containing parenthesized version constraints (and one extras+marker case).
manifests_test.go	Adds regression test validating end-to-end parsing and PURL generation for the new fixture.
internal/pypi/pypi.go	Adjusts parsePEP508 to handle optional parentheses around version constraints.
internal/pypi/pypi_test.go	Extends unit tests for parsePEP508 and adds a benchmark covering representative inputs.

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