feat(delete): per-directory delete plans for --delete-during/--delete-delay (protocol 2.24.0)

Stream one delete plan per source directory from sender to receiver instead of
a single whole-tree keep-set manifest:

- --delete-during applies each directory's extras as its plan arrives, before
  that directory's data (rsync's generator-order deletion).
- --delete-delay snapshots each directory's extras while the plan arrives and
  commits the removals only after a fully-successful transfer, so files created
  after the scan survive (matching rsync's delete-delay, not delete-after).
- Type conflicts (a destination file blocking a source directory, or vice
  versa) are cleared immediately in both modes, so the nested write succeeds.

The plan carries the destination-relative directory, its kept child directory
names and its kept child file names; the first frame also carries the global
protected prefixes, size-skipped prefixes and --delete-missing-args paths.
--delete-before keeps the existing whole-tree early manifest; plain --delete and
--delete-after keep the end-of-transfer manifest commit.

Preserves the existing safety surface: protected/size-skipped prefixes and the
--delay-updates/basis skips are honored at any depth, deletion is scoped to the
synchronized directories (--files-from), MAX_SERVER_DELETE_COUNT and
--max-delete (partial + exit 25) are shared across plans, symlinks are never
followed, and paths are confined to the receive root.

src/shared/file_receive.h

@@ -118,6 +118,14 @@ bool manifest_delete_extras(const Config* config, DeleteManifest* manifest);
    confinement or I/O error (the run then fails); tolerated per-path cases are
    reported and skipped. */
 bool manifest_delete_missing_args(const Config* config, DeleteManifest* manifest);
+/* Budgeted form of manifest_delete_missing_args for the per-directory delete
+   session: each removed mirror draws from `max_delete` (SIZE_MAX = unlimited)
+   and the tallies are accumulated into `*deleted`/`*skipped`.  `*limit_hit` is set
+   when the budget stopped the pass with entries left over.  Returns false only
+   on a genuine deletion error. */
+bool manifest_delete_missing_args_limited(const Config* config, DeleteManifest* manifest,
+                                          size_t max_delete, size_t* deleted, size_t* skipped,
+                                          bool* limit_hit);
 /* Outcome of committing a delete manifest.  LIMIT_REACHED reports rsync's
    partial --max-delete result: the budget allowed some deletions and the rest
    were skipped (the run still stores all file data but the client exits 25). */