Description

Follow-up to #2973, which fixed __hash__ for Role and DelegatedRole.

Same problem was still there in the other metadata classes: Signed, Root, MetaFile, Snapshot, Delegations, TargetFile, Targets, and Metadata. Their __hash__ implementations passed raw dictionaries into hash(), which throws TypeError: unhashable type: 'dict'.

Timestamp.__hash__ looked fine on its own, but still breaks because it inherits from Signed and MetaFile.

All these classes define __eq__, so they need a working __hash__ too if they're going to be used in sets or as dict keys. test_metadata_eq_.py covers equality for these classes but never tested hashing, which is probably why this slipped through.

Fix follows the same approach as #2973 — hash a subset of immutable fields instead of the raw dicts.

unrecognized_fields is left out since it can hold arbitrary nested JSON. Everything else I just converted to tuples.

Testing

• test_metadata_hash checks that for each affected class, hash() doesn't raise, equal objects produce equal hashes, and instances can be used as set members. This fails on develop with 8 subtest errors before the fix.
• test_metadata_hash_ignores_unrecognized_fields checks the deliberate exclusion of unrecognized_fields — objects that only differ in that field are unequal but can share a hash, which is fine given the data model.