docs(py): update PARITY_AUDIT.md with PR status, middleware taxonomy, and merge order

Comprehensive update reflecting current state of all merged and open PRs:

Merged PRs reflected:
- #4511 (G5+G6: span_id + X-Genkit-Span-Id) → marked Done
- #4507+#4508 (G11: CHANGELOG.md) → marked Done
- #4509 (plugin test coverage uplift) → marked Done
- #4505 (PARITY_AUDIT.md baseline) → marked Done
- #4488 (sample naming, py.typed, check_consistency) → marked Done

Open PRs tracked:
- #4516 (G1+G2: model middleware storage)
- #4514 (Transfer-Encoding fix)
- #4513 (G18: multipart tools)
- #4512 (G20-G22: constructor parity)
- #4510 (G3+G12-G16: middleware functions)
- #4504 (Checks plugin)
- #4495, #4494, #4401 (bug fixes + reflection v2)

New content:
- Middleware Taxonomy section with 4-layer diagram
- Decision guide for which middleware layer to use
- G38 gap (auto-wiring via get_model_middleware)
- PR merge order graph with file conflict matrix
- Updated summary metrics and phase tables

fix: address review comments — fix G1/G2 status consistency, middleware level count, #4514 merged

docs(py): update PARITY_AUDIT.md — mark #4494 and #4514 merged, add #4518 Cohere

Update PR status tracking:
- #4494 (RedactedSpan fix): marked merged
- #4514 (Transfer-Encoding fix): marked merged
- #4518 (Cohere provider plugin): added as open PR
- Updated dependency chain, summary metrics, and open PR counts

docs(py): update PARITY_AUDIT.md — add #4519 (Core fix)

docs(py): update PARITY_AUDIT.md with latest merged PR status

Rationale: Several PRs have merged since the last update. This
syncs the document with the current state of all PRs.

Changes:
- Mark #4495, #4518, #4520 as merged in all tables
- Move #4495, #4518 from INDEPENDENT to MERGED in dependency chain
- Add #4520 (converter extraction) to merged list
- Update summary metrics: 6 open PRs (down from 8)
- Simplify Layer 3 deps since #4495 is now merged

docs(py): add issue tracker analysis, dependency graph, model conformance roadmap, and sample flow test plan

Rationale:
Comprehensive update to PARITY_AUDIT.md with 5 new sections (§12–§16) covering:
- Cross-SDK issue tracker analysis verified against Python source code
- Dependency-aware reverse topological sort roadmap for prioritized fixes
- Model conformance testing roadmap with provider parity matrix
- Sample flow test plan with optimal execution order for error detection

Changes:
- §12: Fixability assessment of 9 'likely' issues with code-level verdicts
- §13: Dependency graph (W1–W14), file conflict matrix, PR manifest with
  regression test specifications, sprint-based execution plan
- §14: Model conformance roadmap (Phases 0–4), plugin parity matrix,
  conformance PR mapping, JS-only plugin gaps
- §15: Combined roadmap unifying parity gaps, issue fixes, and conformance
- §16: Sample flow test plan with 5-phase error detection priority pyramid,
  36 samples ordered by feature coverage, quick-start commands, and env
  var reference table

docs(py): add active RFC redesigns (Middleware V2, Bidi, Agent) to parity audit

- Add 7 new gaps (G38-G44) for Middleware V2, Bidi Action/Flow/Model,
  Agent primitive, Plugin V2, and Reflection API V2
- Mark middleware gaps G1-G3, G12-G16 as PAUSED (blocked on upstream
  JS #4515 and Go #4422 Middleware V2 RFCs)
- Mark G19 (Model API V2) as SUPERSEDED by G38 + G41
- Add deep-dive sections §8l-8p covering all 5 active RFC designs
- Update dependency graph: critical path now G38→G2→G1→G3 (4 levels)
- Restructure phased roadmap: Phase 1 (unblocked), Phase 2-3 (paused),
  Phase 4 (bidi/agent, blocked), Phase 5 (integration), Phase 6 (deferred)
- Update §5g cross-SDK gaps table with new primitives
- Update §9b status tracker and §9c dependency matrix
- Update summary metrics: 36 total gaps, 8 paused, 6 upstream-blocked

docs(py): update PARITY_AUDIT.md PR status to 2026-02-11

Comprehensive status update reflecting 23 PRs merged since last
update (2026-02-09), 3 PRs closed/superseded, and 11 currently
open PRs including releasekit tooling, dotprompt fixes, and CI
workflow migration.

Key changes:
- §14f: Checks plugin marked as merged (#4504)
- §15b: Split into Recently Merged / Closed / Currently Open
- §15c: Updated metrics (31 merged, 11 open, 3 closed)
- Added releasekit PRs (14 merged, 3 open) as new workstream

Author: yesudeep