geolocation: add cross-language borsh fixture tests

[0xzrf]

Summary of Changes

• Added cross-language fixture coverage for the geolocation Go SDK by introducing a Rust fixture generator and Go fixture tests.
• The Rust generator (sdk/geolocation/testdata/fixtures/generate-fixtures) serializes real onchain Rust structs via Borsh and writes paired .bin + .json fixtures for:
  • GeolocationProgramConfig
  • GeoProbe
  • GeolocationUser (including targets and result_destination)
• Added Go fixture tests (sdk/geolocation/go/fixture_test.go) that load those fixtures, deserialize using the Go SDK, and validate field-by-field values against the JSON sidecars.
• Wired the new generator and tests into repo workflows:
  • make generate-fixtures now generates geolocation fixtures
  • make sdk-test now runs go test ./sdk/geolocation/go/...
  • excluded the generator crate from the root Cargo workspace to match existing fixture-generator conventions
• Why this is necessary: Go-only round-trip tests can miss subtle Rust↔Go Borsh incompatibilities; fixture tests ensure the Go SDK can deserialize authoritative Rust-produced bytes, preventing regressions and onchain decoding failures.
• Metrics exposed: None.
• Supporting docs / external resources: Issue: #3306.
• CHANGELOG.md update needed: No.

Testing Verification

• make generate-fixtures
• go test ./sdk/geolocation/go/...
• make sdk-test