Fix #751: include the full generator definition in the cache hash

[phverg]

Problem

Fixes #751.

Ttptttg._sha256_input_yaml_hexdigest hashes only {parameters, vlnv, gapi} from generator_input. Editing the generator — whether by pointing command:/interpreter: at a different file or by editing the script's bytes in place — leaves the hash identical, so subsequent runs silently serve the previously-cached output even though the program that produced it has changed.

Solution

Fold the generator definition into the hash: command, interpreter, and a SHA-256 of the resolved script bytes. A clean rebuild now happens whenever any of these changes.

Why slightly broader than the literal ask in the issue: "the command being executed" naturally includes the script content, not just the declared path. Hashing only the declared command: string catches renames but not in-place script edits — which is the common "I updated the generator and the cache still served stale output" symptom. Hashing the resolved bytes closes that gap and mirrors the pattern PR #777 uses for provider patch bytes.

Deliberately NOT hashed:

• The resolved interpreter path from shutil.which(interpreter). That depends on the system PATH at run time and is not part of the generator definition the user signs in their .core file. The interpreter name is what we sign.
• The generator's root path. It's an absolute path that differs between machines and checkouts, which would make cache directory names environment-specific and the test reference hashes machine-specific. Two generators with the same relative command rooted under different directories are still distinguished by the script bytes hash: if their bytes differ, the cache differs; if their bytes match, sharing the cache is the desired behaviour.

This necessarily invalidates existing on-disk caches for cacheable generators on first run after upgrade (the directory name embeds the hash). Users get one extra regeneration and consistent behaviour afterwards. The hardcoded reference hashes in test_generators are updated accordingly.

Test plan

• test_generator_input_hash_includes_command — proves changing command flips the hash; stable across repeats.
• test_generator_input_hash_includes_interpreter — proves swapping python3 → python2 flips the hash.
• test_generator_input_hash_includes_script_bytes — missing → v1 → v2 → v1-again sequence, proving the hash depends on bytes not on mtime.
• Existing test_generators reference hashes updated; full tests/test_edalizer.py green (7 passed).
• pre-commit run -a clean.