Build with Zig 0.15.2 and bump googletest

[fng97]

This includes the following changes:

1. Updates build.zig to build with Zig 0.15.2
2. Bumps the googletest dependency to 1.17.0
3. Adds a step for building the bundled samples
4. Adds building the samples to CI
5. Updates the action versions in build.yml
6. Adds a README

I expect the checks will fail because they're using the workflow defined in main which uses Zig 0.13.0. You can find a passing CI run on my fork.

[fng97]

Just noticed the other PRs. Included @LukasKastern's addition of gmock in #2.

[mattnite]

Closes #2, #3, #4