build: pin vendored zstd to released v1.5.7

No v1.6.0 release exists upstream (dev-branch changelog only); the submodule
was tracking dev. Pin to tag v1.5.7 — the latest release — for a reproducible,
released codebase.

- third_party/zstd → v1.5.7 (ZSTD_VERSION 1.5.7)
- README badge + docs/supported.md version → 1.5.7
- public symbol count 186 → 185 (drop ZSTD_isDeterministicBuild, a 1.6.0-dev
  addition); Misc/experimental 0/11 → 0/10
- deprecated set unchanged (25); all 55 bound symbols present; 114 tests green

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: dfa1

README.md

@@ -1,7 +1,7 @@
 # zstd-java
 
 [![CI](https://github.com/dfa1/zstd-java/actions/workflows/ci.yml/badge.svg)](https://github.com/dfa1/zstd-java/actions/workflows/ci.yml)
-![zstd](https://img.shields.io/badge/zstd-1.6.0-green.svg)
+![zstd](https://img.shields.io/badge/zstd-1.5.7-green.svg)
 ![Java](https://img.shields.io/badge/Java-25%2B-orange.svg)
 [![License](https://img.shields.io/badge/License-BSD%203--Clause-blue.svg)](LICENSE)
 

docs/supported.md

@@ -3,8 +3,8 @@
 Coverage of the zstd C API by the `io.github.dfa1.zstd` bindings. Signatures
 and semantics follow the [official manual](https://facebook.github.io/zstd/doc/api_manual_latest.html).
 
-- zstd version: **1.6.0** (vendored `third_party/zstd`)
-- Public symbols exported by `libzstd`: **186**
+- zstd version: **1.5.7** (vendored `third_party/zstd`, pinned to tag `v1.5.7`)
+- Public symbols exported by `libzstd`: **185**
 - Bound so far: **55** (~30%)
 
 "Bound" means the symbol has a `MethodHandle` in `Bindings` and is reachable
@@ -38,7 +38,7 @@ rather than the deprecated `ZSTD_getDecompressedSize`.
 | Memory sizing | 0 / 14 | `sizeof_*` / `estimate*` accounting not bound |
 | Low-level block | 0 / 12 | expert block/continue API not bound |
 | Sequences | 0 / 5 | sequence producer API not bound |
-| Misc / experimental | 0 / 11 | static-buffer init, param helpers, `copy*` not bound |
+| Misc / experimental | 0 / 10 | static-buffer init, param helpers, `copy*` not bound |
 
 ## Bound symbols → Java
 
@@ -333,7 +333,7 @@ sequence-producer hooks vs this library's frame-inspection and typed-error surfa
 | `ZSTD_mergeBlockDelimiters` | — | — |
 | `ZSTD_registerSequenceProducer` | — | ✅ |
 
-### Misc / experimental (0/11)
+### Misc / experimental (0/10)
 
 | Symbol | Bound | zstd-jni |
 |---|:---:|:---:|
@@ -347,4 +347,3 @@ sequence-producer hooks vs this library's frame-inspection and typed-error surfa
 | `ZSTD_initStaticCDict` | — | — |
 | `ZSTD_initStaticDCtx` | — | — |
 | `ZSTD_initStaticDDict` | — | — |
-| `ZSTD_isDeterministicBuild` | — | — |