Update Starlette dependency to >=0.49.1

[ColeMurray]

Summary

Updates the Starlette dependency constraint from >=0.27 to >=0.49.1 across the main project and example servers to address security vulnerabilities in earlier versions.

Changes

• Updated pyproject.toml to require Starlette >=0.49.1
• Updated example server dependencies in:
  • examples/servers/simple-streamablehttp/pyproject.toml
  • examples/servers/simple-streamablehttp-stateless/pyproject.toml
• Updated uv.lock to reflect the new dependency version (0.49.1)

Test Plan

• Formatting checks pass (ruff format)
• Linting checks pass (ruff check)
• Type checking passes (pyright)
• CI tests will run automatically

[Kludex]

Same as:

• mitigate CVE-2025-62727 for starlette #1552
• Update Starlette to 0.49.1 in uv.lock #1559