fix: avoid scheduler descriptor side effects (v26.09.11)

[ancongui]

Summary

Scanning a Pydantic settings bean in TaskScheduler.discover() evaluated deprecated instance descriptors and emitted two PydanticDeprecatedSince211 warnings in the published 26.9.10 wheel. The scheduler now uses the existing application-context descriptor guard before binding methods, without warning suppression. Ordinary, inherited, static and class scheduled methods remain discoverable and executable.

This patch adds two regressions, documents the discovery contract, and updates release metadata to v26.09.11 (package 26.9.11). It introduces no public API or configuration changes.

Type of Change

• Bug fix
• Documentation

Test Plan

• Full local suite: 7,727 passed, 6 skipped, 2,573 marker-deselected; 85% coverage.
• GitHub CI passed: Python 3.12/3.13, SQLAlchemy 2.0, lint, types, docs/book, build, browser and installed distributions.
• Both new regressions fail before the fix and pass afterward.
• Existing scheduler tests plus regressions: 17 passed.
• Ruff lint/format and strict mypy: passed (782 source files).
• Strict documentation build and wheel/sdist build: passed.
• Isolated installed wheel with Pydantic 2.13.5: four scheduled bindings invoke correctly with zero Pydantic warnings.