Split tests from binary builds and skip build workflow on docs only changes

[Aswinr24]

Issue

build.yml runs tests and also builds binaries (Linux x86/arm64 + Windows) on all pushes and PRs

Proposed change

1. Split workflows:

   • Create a seperate lightweight workflow that runs unit tests
   • Keep build.yml focused on building and release of binaries

2. Add path filtering to the build workflow:

   • Add paths-ignore filters so the workflow doesn’t run when docs only changes are made