test: Link unit tests with nginx library.

[ensh63]

Proposed changes

Some unit tests may use C functions from nginx. To support this scenario, special static library is built. Necessary linker flags are also added. Since these changes are needed for specific unit tests only, new feature "unittest" is defined in nginx-sys and nginx-src crates.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have written my commit messages in the Conventional Commits format.
• I have read the CONTRIBUTING doc
• I have added tests (when possible) that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[Copilot]

Pull Request Overview

This PR adds support for linking unit tests with nginx library by introducing a new "unittest" feature flag and building a static nginx library. The changes enable unit tests to use C functions from nginx by creating a special static library (libnginx) and adding necessary linker flags when the unittest feature is enabled.

• Introduces a new "unittest" feature flag for nginx-sys and nginx-src crates
• Creates a libnginx module with helper functions for nginx initialization in tests
• Adds build configuration to generate static nginx library and parse linker flags

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/core/pool.rs	Adds comprehensive unit tests for Pool functionality using nginx C functions
nginx-sys/build/main.rs	Extends makefile parsing to extract library flags and adds unittest feature support
nginx-sys/Cargo.toml	Defines unittest feature dependency on vendored nginx-src
nginx-src/src/lib.rs	Configures nginx build to include libnginx module when unittest feature is enabled
nginx-src/libnginx/	New module providing C wrapper functions for nginx initialization in tests
Cargo.toml	Adds nginx-sys with unittest feature as dev dependency

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