feat(stellar): integrate on-chain metadata resolver for wraith-names

[OTimileyin]

Closes #119

Summary

Add optional on-chain metadata resolver for wraith-names, allowing name
owners to attach text records and content hashes to their .wraith names,
similar to ENS text records. The feature is opt-in, owner-gated, and avoids
the resolution hot path.

Changes

New: src/metadata.rs

• MetadataEntry struct with text_records: Map<String, String> and
  content_hash: BytesN<32>
• MetadataError enum with 5 dedicated error codes (101–105):
  MetadataKeyTooLong, MetadataValueTooLong, MetadataRecordTooLong,
  MetadataTotalTooLong, MetadataNotFound
• Validation functions with per-record (key ≤ 64B, value ≤ 256B) and total
  (≤ 1024B) size limits
• Unit tests for validation logic

Modified: src/lib.rs

• DataKey::Metadata(BytesN<32>) storage key variant for per-name metadata
• 5 new NamesError variants (50–54) for metadata error propagation
• set_metadata(env, owner, name, metadata) — owner-gated setter with full
  validation
• get_metadata(env, name) — public reader, returns NameNotFound or
  MetadataNotFound
• Metadata cleanup on release() — metadata is removed when a name is
  released
• MetadataUpdated event emission on metadata changes

Hot path untouched

• resolve() and name_of() remain completely unchanged — no metadata
  lookups added to the resolution path

Tests

• test_set_and_get_metadata — happy path with avatar + twitter records
• test_set_metadata_not_owner — non-owner rejected with NotOwner
• test_set_metadata_key_too_long — 65B key → MetadataKeyTooLong
• test_set_metadata_value_too_long — 257B value → MetadataValueTooLong
• test_set_metadata_total_too_long — 5 records × 210B → MetadataTotalTooLong
• test_get_metadata_not_found — name exists, no metadata → MetadataNotFound
• test_get_metadata_unregistered_name — name doesn't exist → NameNotFound
• test_metadata_cleaned_on_release — metadata removed when name is released
• test_hot_path_unchanged_after_metadata — resolve() and name_of() work
  identically before/after metadata
• 3 existing metadata.rs module tests for isolated validation

All 17 wraith-names tests pass, cargo fmt clean, zero warnings.

[truthixify]

This PR is a duplicate of #136 (identical +2626/-116 across the same 13 files). Please close one of them so I only have one to track. Whichever you keep, rebase against develop and retarget the base branch from main to develop (wave PRs go into develop, not main).

[OTimileyin]

Thanks so much I have closed it

[OTimileyin]

@truthixify has it now been resolved?

[truthixify]

Thanks for closing #136. Two things left on this one:

1. The base branch was set back to main (either manually or the earlier retarget got reverted). I retargeted it to develop just now.

2. Retargeting surfaced merge conflicts against develop, since your branch is based off main which has diverged. You will need to rebase your branch on top of latest develop and force-push. Something like:

   git fetch origin
   git rebase origin/develop
   # resolve any conflicts, then
   git push --force-with-lease
   

Once the rebase is clean, CI will re-run and I will merge.