fix: shorten tool names for client limits

[Torch4084]

Summary

• shorten generated tool names when the configured MCP server name would push clients past the 60-character combined limit
• preserve deterministic names using a hash suffix and update operation_map to use the shortened names
• add regression tests for both tool registration and tool execution with shortened names

Fixes #64

Validation

• uv run ruff check fastapi_mcp/server.py tests/test_configuration.py tests/test_mcp_execute_api_tool.py
• uv run pytest --no-cov tests/test_configuration.py tests/test_mcp_execute_api_tool.py