feat(checker): examples() and spec_files() carry the specification's files

A consumer of the checker crate needs no path into this repository.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

target/debug/.fingerprint/proc-macro2-ef41e94ab0f532d9/run-build-script-build-script-build.json

@@ -0,0 +1 @@
+{"rustc":11835527281324007204,"features":"","declared_features":"","target":0,"profile":0,"path":0,"deps":[[16346726298725429545,"build_script_build",false,4525086428172690723]],"local":[{"RerunIfChanged":{"output":"debug/build/proc-macro2-ef41e94ab0f532d9/output","paths":["src/probe/proc_macro_span.rs","src/probe/proc_macro_span_location.rs","src/probe/proc_macro_span_file.rs"]}},{"RerunIfEnvChanged":{"var":"RUSTC_BOOTSTRAP","val":null}}],"rustflags":[],"config":0,"compile_kind":0}