feat(format): bzip2 filter (307), read and write, pure Rust

hdf5plugin's BZip2 failed with UnsupportedFilter(307). The new `bzip2`
feature decodes the single bzip2 stream H5Zbzip2.c stores, bounded by the
chunk size (a truncated stream is an error, not short data), and encodes
at block size cd_values[0] (DatasetBuilder::with_bzip2(level)). It uses the
bzip2 crate's default backend, libbz2-rs-sys, a pure-Rust port of
libbzip2: `cargo tree` shows no cc/cmake, and nothing is compiled from C.

Interop: hdf5plugin writes block sizes 9, 1 and 5+shuffle over the
12-case matrix, read byte for byte; ours at 9 (shuffled) and 1 (not)
reads back through hdf5plugin. Both fail with the decoder removed.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-format/src/chunked_write.rs

@@ -12,8 +12,9 @@ use crate::chunk_grid::ChunkGrid;
 use crate::ea_writer;
 use crate::error::FormatError;
 use crate::filter_pipeline::{
-    FILTER_BITSHUFFLE, FILTER_DEFLATE, FILTER_FLETCHER32, FILTER_LZ4, FILTER_LZF, FILTER_PCODEC,
-    FILTER_PCODEC_NAME, FILTER_SHUFFLE, FILTER_ZSTD, FilterDescription, FilterPipeline,
+    FILTER_BITSHUFFLE, FILTER_BZIP2, FILTER_DEFLATE, FILTER_FLETCHER32, FILTER_LZ4, FILTER_LZF,
+    FILTER_PCODEC, FILTER_PCODEC_NAME, FILTER_SHUFFLE, FILTER_ZSTD, FilterDescription,
+    FilterPipeline,
 };
 use crate::filters::compress_chunk;
 /// Round a file offset up to the next cache-line boundary.
@@ -70,6 +71,12 @@ pub enum PluginFilter {
         /// Compression after the transpose.
         compression: BitshuffleCompression,
     },
+    /// bzip2 (filter 307) at block size `level` (1-9). Needs the `bzip2`
+    /// feature.
+    Bzip2 {
+        /// Block size 1-9 (9 = hdf5plugin's default).
+        level: u32,
+    },
 }
 
 /// What bitshuffle compresses its blocks with.
@@ -94,6 +101,7 @@ impl PluginFilter {
         match self {
             PluginFilter::Lzf => false,
             PluginFilter::Bitshuffle { .. } => true,
+            PluginFilter::Bzip2 { .. } => false,
         }
     }
 
@@ -112,6 +120,12 @@ impl PluginFilter {
             },
             // bshuf_h5_set_local: version 0.4, element size, block size,
             // compression (0 none, 2 LZ4, 3 Zstandard), Zstandard level.
+            PluginFilter::Bzip2 { level } => FilterDescription {
+                filter_id: FILTER_BZIP2,
+                name: Some("bzip2".into()),
+                flags: 1,
+                client_data: vec![(*level).clamp(1, 9)],
+            },
             PluginFilter::Bitshuffle {
                 block_size,
                 compression,