Feat/graceful shutdownfeat: expose /internal/buildinfo endpoint for version and runtime diagnostics

[Luchistack]

#closes #891

Description

Implemented the GET /internal/buildinfo endpoint to expose version, commit, build time, and Go runtime/compiler information. This simplifies incident triage, version tracking, and canary deployments.

Changes Made:

• Handler Implementation: Added GetBuildInfo in internal/handlers/buildinfo.go utilizing runtime/debug.BuildInfo and runtime package stats with fallback handling for non-VCS/development builds.
• Testing: Added comprehensive unit tests in internal/handlers/buildinfo_test.go verifying response correctness and maintaining >95% package coverage.

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Ran unit tests locally via go test ./internal/handlers/... -cover confirming 100% test success and coverage thresholds.

#closes

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[ayomideadeniran]

pr under review