feat(p7-cli-namespace): rename colliding short flags to rsync parity (Wave A)

-c -> --checksum, -m -> --prune-empty-dirs, -M -> --remote-option,
-f -> --filter, -s -> --secluded-args, -p -> --perms, -T -> --temp-dir;
-a/--archive is now real rsync -rlptgoD (links+metadata+devices+specials).

FastSync's own flags moved to long-form-only or new shorts:
-j/--threads (multithreading), --preserve (metadata), --sendfile,
--chunk-serialization, --timeout, --ssh-port. Client-side only; the
wire config fields are unchanged (no PROTOCOL_VERSION bump). The server
keeps -p as its port. Docs (README, RSYNC_COMPAT summary 129->132) and
unit/integration tests updated. 37/37 unit, 400-pass integration.

tests/integration/test_iconv.py

@@ -243,7 +243,7 @@ def test_iconv_chunk_serialization_blob(shared_server):
     _place_bytes(source, name, data=b"blob\n")
 
     result, _ = run_client(
-        source, dest, flags=["--iconv=iso-8859-1,utf-8", "-s"], port=shared_server.port
+        source, dest, flags=["--iconv=iso-8859-1,utf-8", "--chunk-serialization"], port=shared_server.port
     )
     assert result.returncode == 0, (result.stderr or result.stdout)[:400]