perf: lazy-load MCP SDK and event types to reduce cold start by ~29%

[iris-clawd]

Summary

Reduces import crewai cold start time by lazy-loading heavy dependencies that aren't needed at import time.

Baseline: ~4.7s → After: ~3.4s (warm cache, ~29% improvement)

Changes

1. Fix MCP import path in agent/core.py

• Changed from crewai.mcp import MCPServerConfig → from crewai.mcp.config import MCPServerConfig
• This avoids triggering mcp/__init__.py which eagerly loaded the full mcp SDK (~400ms)
• Moved MCPToolResolver import into get_mcp_tools() method body (only needed at runtime)

2. Lazy-load heavy MCP imports in mcp/__init__.py

• MCPClient, MCPToolResolver, BaseTransport, TransportType now use __getattr__ lazy loading
• Lightweight config/filter types remain eagerly imported
• Follows the same pattern already used in crewai/__init__.py for Memory

3. Lazy-load all event type modules in events/__init__.py

• Previously only agent_events were lazy-loaded; now all 12 event type modules are lazy
• events/__init__.py runs whenever ANY crewai.events.* submodule is accessed (Python package init), so this prevents loading ~12 Pydantic model modules unnecessarily
• TYPE_CHECKING imports preserved for IDE/type-checker support
• __all__ unchanged — public API is identical

What's NOT changed (intentionally)

• Flow — too deeply entangled (model_rebuild, Entity union type)
• Knowledge/chromadb — needs storage-layer refactoring (separate PR)
• A2A config — needed by model_rebuild for Pydantic field resolution

Testing

• python -c 'import crewai' — ✅ works
• from crewai.events import CrewKickoffStartedEvent, LLMCallStartedEvent, ... — ✅ lazy resolution works
• from crewai.events import crewai_event_bus, BaseEventListener — ✅ core imports unchanged
• All existing __all__ exports preserved

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Note

Medium Risk
Moderate risk because it changes import-time behavior via __getattr__ lazy loading in public packages, which can surface subtle runtime import/order issues; also updates dependency pins (notably lxml) that could affect optional integrations.

Overview
Improves import crewai performance by avoiding heavy imports at package init: crewai.mcp now lazy-loads MCPClient/MCPToolResolver/transport types, crewai.events lazy-loads all event type classes (not just agent events), and Agent.get_mcp_tools() defers importing MCPToolResolver while switching MCPServerConfig to import from crewai.mcp.config.

Adds a new GitHub Actions workflow (import-time.yml) that benchmarks import crewai on the PR vs base branch and fails if median import time regresses by more than 5%. Also updates tooling/deps: bumps lxml in crewai-tools optional rag extras for a security advisory, adjusts [tool.uv].exclude-newer, and ignores UNKNOWN.egg-info/ in .gitignore.

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