Remove un-accepted RFCs from develop (#47)

## Summary
- Removes 4 RFCs that were merged as "proposed" under the old directory
structure but never formally accepted
- RFC 0005 (Extension Types), RFC 0023 (File compat testing), RFC 0029
(Type system), RFC 0033 (Block TurboQuant)
- These will be re-proposed as separate PRs after this merges

## Test plan
- [ ] Build still passes with remaining RFCs
- [ ] Merge, then open 4 new PRs to re-add each RFC

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gatesn