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/bookspec-runner-1becf402983b72ae/lib-bookspec_runner.json

@@ -0,0 +1 @@
+{"rustc":11835527281324007204,"features":"[]","declared_features":"[]","target":12310434289865374525,"profile":1045304723318631657,"path":14747602201717508755,"deps":[[8160210889872729633,"serde_json",false,15000670766945111310],[15417218606223624986,"bookspec_checker",false,17774672925137196404]],"local":[{"CheckDepInfo":{"dep_info":"debug/.fingerprint/bookspec-runner-1becf402983b72ae/dep-lib-bookspec_runner","checksum":false}}],"rustflags":[],"config":9396254390672932401,"compile_kind":0}