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/num-traits-71a2e43671297104/run-build-script-build-script-build

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+a170e1b7037a16cd

target/debug/.fingerprint/num-traits-71a2e43671297104/run-build-script-build-script-build.json

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+{"rustc":11835527281324007204,"features":"","declared_features":"","target":0,"profile":0,"path":0,"deps":[[5157631553186200874,"build_script_build",false,16269571480882087456]],"local":[{"RerunIfChanged":{"output":"debug/build/num-traits-71a2e43671297104/output","paths":["build.rs"]}}],"rustflags":[],"config":0,"compile_kind":0}