Fix OCaml 5.4 compatibility across the monorepo
- Rename `effect` variable to `eff` in editor.ml (reserved keyword in 5.4)
- Add `first_crc` cppo-guarded helper for cmi_crcs API difference
(Import_info.t array in oxcaml vs (string * Digest.t option) list in 5.4)
- Remove `source_rendering` from dune-workspace (not in upstream dune/odoc)
All extension packages, tessera, zarr, and odoc now build with both
oxcaml 5.2.0+ox and standard OCaml 5.4.1. The js_top_worker library
compiles on both; linking requires matching merlin-lib.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>