refactor: prune dead provider helpers and collapse SlotEntities builders

[raman325]

Proposed change

Mechanical cleanups surfaced by an audit of providers/_util.py and websocket.py — net -87 lines across production + tests, zero behavior change.

providers/_util.py

• Delete make_legacy_tagged_name — zero non-test callers; the providers it was reserved for already emit the canonical lcm:<slot>: format.
• Inline parse_tag_with_rewrite into parse_tag — single caller, vestigial needs_rewrite boolean (no consumer ever flipped on it).
• Legacy [LCM:<slot>] is now strictly read-only: parse_tag still recognizes it so older lock-stored names continue to identify as LCM-owned until the next write rewrites them in canonical form.

websocket.py

• Extract _build_slot_entities(ent_reg, entry_id, slot_num) — the per-lock iterator (_get_slot_entity_ids) and the per-slot subscription resolver now share one unique_id formula and one populated SlotEntities shape (the two previously diverged on config_entry_id vs event_entity_id).
• Drop _get_slot_entity_data — its only call site now invokes _build_slot_entities directly.
• Change _get_slot_metadata() to take pre-resolved entities. _serialize_lock_coordinator was walking the entity registry twice per call (once via _get_slot_metadata, once directly); now it walks once and reuses.

Tests

• Port the rich match-priority cases from TestParseTagWithRewrite onto TestParseTag (adapted to 2-tuple). No coverage loss for parse_tag.
• test_websocket mocks updated from _get_slot_entity_data to _build_slot_entities.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionality)
• Code quality improvements to existing code or addition of tests

Additional information

Surfaced by a codebase-wide audit for unnecessary complexity. Larger items found in the same audit (parallel circuit breakers in coordinator vs sync, twin confirmation paths, _verified + _pending_writes parallel state) are intentionally not part of this PR — they need a design call, not a mechanical refactor.

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Local tests pass. Your PR cannot be merged unless tests pass

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.16%. Comparing base (4657eab) to head (6d17239).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1266   +/-   ##
=======================================
  Coverage   97.15%   97.16%           
=======================================
  Files          54       54           
  Lines        6543     6521   -22     
  Branches      460      460           
=======================================
- Hits         6357     6336   -21     
+ Misses        186      185    -1     

Flag	Coverage Δ
python	97.71% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...om_components/lock_code_manager/providers/_util.py	100.00% <100.00%> (ø)
custom_components/lock_code_manager/websocket.py	98.23% <100.00%> (+0.16%)	⬆️

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