fix(lint): resolve E205, E331, E405, E415, E600, E605, E715, E718, E725

Standardize fuzz and test conventions across 30+ packages:

- E715/E718: Add fuzz.ml runners referencing Fuzz_*.suite instead of
calling Fuzz_*.run() directly; update dune files accordingly
- E725: Fix fuzz_paseto suite name from "crowbar" to "paseto"
- E600: Create .mli interfaces for test modules (test_firmware,
test_remoteproc, test_pbkdf2, test_paseto) with single-group suites
- E605: Add missing test files (test_skills, test_monitor, test_openamp,
test_xrpc_server) with proper module extraction from inline test.ml
- E415: Add pp pretty-printer to xrpc_server type t
- E405: Add doc comment for pp_sync_action in skills.mli
- E205: Replace Printf with Fmt in fuzz_paseto and gen_corpus
- E331: Rename make_key to key in fuzz_paseto