chore: bump to 1.2.1, pympp 0.7.0, pytempo 0.5.1 (#6)

## Summary

- pympp 0.6.0 → 0.7.0 (within existing `>=0.6,<1` bound)
- pytempo 0.5.0 → 0.5.1 (patch)
- Both are `[project.optional-dependencies]` — published distribution
only re-resolves when users install `agentscore-commerce[mppx,x402]`.
- Version: 1.2.0 → 1.2.1

## Test plan

- [x] Local typecheck + tests pass (lefthook pre-push)
- [ ] After merge: tag `v1.2.1` to publish to PyPI

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vvillait88

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "agentscore-commerce"
-version = "1.2.0"
+version = "1.2.1"
 description = "Agent commerce SDK for Python — identity middleware (FastAPI, Flask, Django, AIOHTTP, Sanic, ASGI) + payment helpers + 402 builders + discovery + Stripe multichain. The full merchant-side toolkit for AgentScore-powered agent commerce."
 readme = "README.md"
 license = "MIT"