refactor: Refactor builder registry

[OCopping]

Summary

Refactors the entity registry from root-PV-keyed to full-PV-keyed, enabling both direct lookups (e.g. BL19I-MO-DCM-01:BRAGG → single motor) and root-prefix lookups (e.g. BL19I-MO-DCM-01 → all motors) through a single helper method.

This supports a stripped-down techui.yaml where only custom components need explicit entries, while simple components are auto-discovered by root PV.

Changes

• models.py — Added Entity.base_prefix computed property
• builder.py — entities changed from defaultdict[str, list[Entity]] → dict[str, Entity]; new get_entities_for_prefix() helper that collects from exact match + root-prefix children; create_screens() updated to use it
• tests/ — Updated entity lookups for the new dict structure; added builder_with_entities fixture and 4 tests covering single match, root+children, no-match, and root-without-root-entity

[codecov]

Codecov Report

❌ Patch coverage is 95.08197% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.27%. Comparing base (2dd3dc6) to head (5f7aa91).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/techui_builder/generate.py	91.30%	2 Missing ⚠️
src/techui_builder/builder.py	96.55%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #276      +/-   ##
==========================================
- Coverage   96.55%   96.27%   -0.29%     
==========================================
  Files          17       17              
  Lines        1075     1101      +26     
==========================================
+ Hits         1038     1060      +22     
- Misses         37       41       +4     

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[Copilot]

Copilot review overview

🟡 Changes recommended

Screen labels leak between mappings, and existing suffixes support mappings lose their overrides.

Review effort: Balanced
Findings: 2

Open (2)

• Reset component label for each screen macro mapping · New
• Preserve or migrate renamed support-map suffixes key · New

What changed in this PR

Refactors entity lookup to use full PV keys while supporting root-prefix discovery.

Changes:

• Adds full-PV entity registration and prefix lookup.
• Introduces typed support-screen mappings.
• Updates generator behavior and tests.

File	Description
src/​techui_builder/​builder.py	Refactors entity storage and lookup.
src/​techui_builder/​models.py	Adds base prefixes and typed screen models.
src/​techui_builder/​generate.py	Uses typed screen mappings and macro overrides.
src/​techui_builder/​utils.py	Defines public module exports.
tests/​conftest.py	Updates fixtures for new models.
tests/​test_builder.py	Tests full and root-prefix lookups.
tests/​test_generate.py	Updates typed screen access.

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[adedamola-sode]

Isn't this already in the previous PR that was approved and merged, is this branched from that?