fix: accept OpenAI tool results without optional name

[thorethy1]

Problem

OpenAI-compatible clients may send a tool-result message with role: "tool", tool_call_id, and content but without name. name is optional in the OpenAI message schema, yet the Python and Rust Message validators required it and rejected an otherwise valid tool-result follow-up.

Fix

• Require tool_call_id for tool messages, but allow name to remain omitted in Python.
• Apply the same validation semantics to Rust; TypeScript already had the desired behavior.
• Keep rejecting tool messages that omit tool_call_id.
• Add regression coverage at the message, provider-conversion, and real /v1/chat/completions HTTP boundaries.

Validation

• Python: 516 passed; MyPy reports no issues in 10 source files.
• TypeScript: build succeeds; 261 passed.
• Rust: cargo fmt --check; 254 passed.
• Ruff: the branch and upstream/main both report the same 22 pre-existing findings; this change introduces 0 new findings.
• git diff --check passes.

Checklist

• The diff is limited to tool-message validation and focused regression tests.
• tool_call_id remains mandatory.
• Optional name behavior is consistent across Python, TypeScript, and Rust.
• A complete assistant tool-call → tool-result HTTP roundtrip without name is covered.
• Python, TypeScript, and Rust test suites pass.
• Formatting, typing, whitespace, and added-line secret/debug scans pass.
• No generated build artifacts, credentials, or unrelated changes are included.