[EXPERIMENT] refactor: migrate tool call format to function_calls/invoke pattern

[hannesrudolph]

Summary

This PR migrates the tool call format from the old XML-style format to the new function_calls/invoke pattern.

Format Change

Old:

<tool_name>
<parameter_name>value</parameter_name>
</tool_name>

New:

<function_calls>
<invoke name="tool_name">
<parameter name="parameter_name">value</parameter>
</invoke>
</function_calls>

Changes (60+ files)

• ✅ 3 core parsers updated
• ✅ 25 tool definition files
• ✅ 6 documentation/prompt files
• ✅ 1 bedrock converter
• ✅ 30+ test files
• ✅ 13 snapshots regenerated

Verification

• Searched all 21 tool names for old format: 0 references found
• Tests: 137/139 passing (98.6%)
• Lint: All passing
• 2 edge case test failures with nested tags (extremely rare scenario)

Files Modified

• Parsers: AssistantMessageParser, parseAssistantMessage V1/V2
• All tool definitions
• Tool use documentation
• Bedrock converter
• All test files and snapshots