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/serde_core-b98c1f9e4c290de7/run-build-script-build-script-build

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+8ae654bd2b320cdf

target/debug/.fingerprint/serde_core-b98c1f9e4c290de7/run-build-script-build-script-build.json

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+{"rustc":11835527281324007204,"features":"","declared_features":"","target":0,"profile":0,"path":0,"deps":[[11029742160753049355,"build_script_build",false,11192661883817782740]],"local":[{"RerunIfChanged":{"output":"debug/build/serde_core-b98c1f9e4c290de7/output","paths":["build.rs"]}}],"rustflags":[],"config":0,"compile_kind":0}