Silence pydantic's benign "schema field shadows BaseModel" startup warning

[devopam]

Summary

• Running MCPg surfaced a wall of UserWarning: Field name "schema" in "..." shadows an attribute in parent "BaseModel" warnings from pydantic on startup / first tools/list.
• Root cause: the mcp SDK's func_metadata.py dynamically builds a pydantic model from each tool's return-type dataclass to publish its outputSchema. Pydantic's BaseModel still carries a deprecated v1-compat .schema() method, and any dataclass field literally named schema (the natural name for "which Postgres schema", used across ~180 tool-return dataclasses in this codebase) collides with it. It's lazy — the warning only fires the first time Tool.output_schema (a cached_property) is accessed, i.e. the first tools/list call, which is why it shows up as soon as a client connects.
• Renaming the field isn't a reasonable fix here — it would change the JSON key in every affected tool's response, a breaking change to the public tool contract, just to quiet a cosmetic startup warning from a deprecated pydantic v1 shim nobody uses.
• Fix: suppress the specific, known-benign message via a scoped warnings.filterwarnings(...) at package import time (src/mcpg/__init__.py), matching only this exact pydantic message pattern (not a blanket UserWarning silence). Also added the same pattern to pyproject.toml's pytest filterwarnings, since pytest resets warnings.filters per test and the runtime filter alone doesn't survive into test collection — without it, the same warning was showing up in every test that touches Tool.output_schema (31+ occurrences in test_tool_surface_snapshot.py alone).

Test plan

• Added test_output_schema_build_emits_no_pydantic_schema_field_shadow_warnings in tests/contract/test_tool_output_schemas.py, which builds the full maximal-flag tool surface fresh inside its own catch_warnings block (pytest resets filters per test, so this re-applies the exact same pattern mcpg exports) and asserts zero shadow warnings.
• Reproduced the warning directly against a real FastMCP server + register_tools() + list_tools() before the fix (18 occurrences), confirmed 0 after.
• uv run pytest -q -m "not integration" — 2624 passed, only one unrelated pre-existing warning (StarletteDeprecationWarning) left in the summary.
• uv run ruff format --check . / uv run ruff check . / uv run mypy src/mcpg — all clean.

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[gemini-code-assist-2]

Code Review

This pull request suppresses Pydantic deprecation warnings regarding fields (like schema) that shadow attributes in the parent BaseModel. It adds a warning filter in src/mcpg/__init__.py, configures pytest in pyproject.toml to ignore these warnings during test collection, and introduces a contract test to verify that no unexpected shadow warnings are leaked during tool output schema generation. I have no feedback to provide.