Upgrade Zig to 0.15.2

[andy1li]

Upgrade Zig to 0.15.2

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Note

Upgrade Zig to 0.15.2 and add a corresponding Dockerfile for builds.

• Infra/build:
  • Upgrade Zig buildpack to zig-0.15.2 in compiled_starters/zig/codecrafters.yml and solutions/zig/01-ry8/code/codecrafters.yml.
  • Add dockerfiles/zig-0.15.2.Dockerfile to install Zig 0.15.2, set PATH/env, build app, and cache .zig-cache.

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