fix(client): close review gaps on list_providers — full shape, pagination, defensive health

[saurabhjain1592]

Summary

Three review-driven fixes on the just-shipped `list_providers()` (PR #164). All three were flagged by the post-merge deep code review:

1. Wire-shape fields — `LLMProvider` was silently dropping `endpoint`, `model`, `region`, `rate_limit`, `timeout_seconds`, and `settings`. SDK callers couldn't introspect provider configuration despite the platform returning all six fields. Surfaced all six. The SDK now matches the platform's `LLMProviderResource` schema.

2. Pagination — `GET /api/v1/llm-providers` is paginated (server-side cap 100, default 20). `list_providers()` ignored that and would silently truncate results in any deployment with more than 20 providers. Added three flavours:

   • `list_providers(page=, page_size=)` — single page, list-shaped return (default no pagination args, server picks defaults)
   • `list_providers_paged(...)` — single page, returns `LLMProviderListResponse` with `pagination` metadata
   • `list_all_providers(...)` — walks every page, default `page_size=100` to minimise round trips

3. Defensive health parsing — a single malformed `health` snapshot on one provider would raise `ValidationError` out of pydantic and crash the entire list call. Wrapped the per-provider health construction in try/except and set `health=None` for the bad row, with a warning logged.

What changed

• `axonflow.types.LLMProvider` — added six optional fields (`endpoint`, `model`, `region`, `rate_limit`, `timeout_seconds`, `settings`)
• New types `PaginationMeta` and `LLMProviderListResponse` (also re-exported from `axonflow`)
• `AxonFlow.list_providers()` accepts `page` / `page_size` kwargs
• New methods `list_providers_paged()` and `list_all_providers()` on both async `AxonFlow` and sync `SyncAxonFlow`
• Per-provider health construction is now defensive (try/except around `LLMProviderHealth(**dict)`)

Test plan

6 new regression tests in `tests/test_list_providers_review_fixes.py`:

• All six optional LLMProvider fields surface when present
• All six fields default to None when absent
• `list_providers_paged` returns `LLMProviderListResponse` with pagination metadata
• `list_all_providers` walks every page and combines results
• Malformed health on one provider does NOT crash the whole listing
• Empty-string `min_sdk_version_for("python")` does NOT trigger the upgrade warning
• Existing 10 tests on `list_providers` + `health_check_detailed` still pass
• `ruff check`, `ruff format --check`, `mypy axonflow` all clean
• Falsey-clobber baseline refreshed

Cross-SDK note

The same review surfaced equivalent gaps in Go / TS / Java SDKs — each will get a sibling PR closing the same shape, pagination, and defensive-parsing concerns.