docs(rust): record latest policy boundaries

Document Rust ownership of compression-size estimator policy and the CLI adaptive feedback state machine, and describe the private C callbacks that remain at those boundaries.

Test Plan:

- Documentation-only change; git diff --cached --check

rust/README.md

@@ -73,7 +73,9 @@ zstd ABI:
     callbacks.
     Public frame-progression dispatch is Rust-owned as well; C projects the
     scalar single-thread inputs and keeps the private MT context behind a
-    callback.
+    callback. Compression-size estimation also uses Rust-owned row-matchfinder
+    mode selection and compression-level budget progression around C-owned
+    parameter construction and workspace-size callbacks.
   - `zstd_compress_params` owns the compression-level tables (formerly
     `clevels.h`), parameter bounds, clamping, validation, table selection,
     source/dictionary adjustment, and match-state/CDict size estimation.
@@ -136,8 +138,9 @@ zstd ABI:
     by the separate `cli/` static-library package only for program archives,
     so library builds do not acquire program-only dependencies.  The C
     `fileio` layer retains the format-specific codec callbacks, private
-    asynchronous-pool adapters, metadata, zstd codec/error mapping, and
-    adaptive-policy integration, while Rust owns the mixed-format probe/dispatch
+    asynchronous-pool adapters, metadata, zstd codec/error mapping, and the
+    adaptive clock/progression and diagnostic callbacks, while Rust owns the
+    mixed-format probe/dispatch
     loop, zstd stream-compression I/O loop, scalar adaptive decisions,
     optional-format decompression loops, decompression result policy/final
     accounting, both shared- and separate-destination multi-file compression
@@ -188,6 +191,9 @@ sequencing, legacy public CDict-begin frame-policy construction and
 unknown-source pledge, and the compressBegin_usingDict family’s unknown-source
 parameter selection and default-level normalization, and public advanced-begin
 parameter validation and init-then-begin ordering now run in Rust.
+Compression-size estimation, including row-matchfinder selection and
+compression-level budget progression, and the CLI adaptive feedback state
+machine also run in Rust behind their private-state callback boundaries.
 CDict advanced private workspace construction, private static-CCtx and
 static-CDict workspace construction and dictionary-content allocation/loading,
 and advanced-CDict dictionary-content loading remain in C. Rust now owns
@@ -197,8 +203,8 @@ scalar CCtx-reset plan, post-match-state storage reservation order, and
 match-state reset policy/order for both CCtx and CDict; C retains
 private layout-size inputs, workspace resize/layout, private field publication,
 and allocator callbacks. Private CCtx reset/matchfinder/workspace operations
-and codec/adaptive-policy
-callbacks remain in C. CDict initialization ordering and scalar publication,
+and codec/adaptive clock, progression-snapshot, and diagnostic callbacks remain
+in C. CDict initialization ordering and scalar publication,
 shared compression-begin dictionary selection, CDict reset attach-versus-copy
 selection, and CDict-begin parameter selection, initialization ordering, and
 source-window policy now run in Rust behind private-state bridges; their C