API Client Libraries - Python, JS, Go, Rust

Description

**THE VIRAL LOOP:**
```
Developer builds custom integration
→ Uses official SDK
→ Integration works reliably
→ Developer's product uses marketplace
→ All users of that product = potential job posters
```

**Why This Works:**
- SDKs enable all other integrations
- Official SDKs = trust
- Multi-language = maximum reach

**Deliverables:**
1. Python: `near-marketplace-py`
2. JavaScript: `@near-marketplace/sdk`
3. Go: `near-marketplace-go`
4. Rust: `near-marketplace-rs`

Each with:
- Full API coverage
- Type definitions
- Error handling
- Rate limiting
- Documentation

**PUBLISHED TO:**
- PyPI, npm, pkg.go.dev, crates.io
- GitHub organizations

**Success Metrics:**
- 200+ total SDK downloads
- Custom integrations built on SDKs