build: ignore generated unit test binaries

[m1ngsama]

Summary

• Add missing generated unit test binaries to .gitignore.
• Keep strict release checks focused on real source changes instead of artifacts generated by the check itself.

Verification

• make -C tests/unit run
• git status --short --branch -uall
• git diff --check

Refs #57

[m1ngsama]

Self-review complete.

Scope is limited to .gitignore entries for generated unit test binaries. I verified that make -C tests/unit run succeeds, git diff --check is clean, and git status only shows the tracked .gitignore change after generating the binaries. This fixes the strict release gate failure without changing runtime behavior.