Split unit test sources into multiple modules

[danielinux]

No description provided.

[Copilot]

Pull request overview

This PR expands and organizes the unit test suite by adding dedicated test translation-unit includes for FIFO/queue behavior and public API/socket/filter behavior, plus a shared unit-test support module, and updates the Makefile to rebuild unit binaries when test sources change and to exclude unit tests from coverage reports.

Changes:

• Added new unit test files for FIFO/queue (unit_tests_fifo.c) and API behavior (unit_tests_api.c).
• Added unit_shared.c to centralize unit-test mocks/helpers and test stack setup.
• Updated Makefile unit/coverage rules to track unit test source dependencies and exclude unit test sources from gcovr output.

Reviewed changes

Copilot reviewed 3 out of 9 changed files in this pull request and generated 2 comments.

File	Description
src/test/unit/unit_tests_fifo.c	Adds additional FIFO/queue edge-case unit tests (wrap/align/full/iteration).
src/test/unit/unit_tests_api.c	Adds extensive unit tests for poll, filter, sockets, DNS helpers, and TCP handshake/RTO behaviors.
src/test/unit/unit_shared.c	Introduces shared mocks/helpers and test packet injection utilities used across unit tests.
Makefile	Attempts to make unit rebuild sensitive to included test sources and adjusts coverage exclude patterns.

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