perf: replace lzma-rs with lzma-rust2 and enable zlib-rs backend

[maboloshi]

Switch LZMA/LZMA2 decoding from lzma-rs to lzma-rust2, and flate2 to the zlib-rs backend

Motivation

While extracting Inno Setup installers (solid LZMA1/LZMA2 chunks and setup-0
blocks) for a Scoop-like package manager, we measured the pure-Rust lzma-rs
decoder to be the dominant cost of decompression. lzma-rust2 is a
maintained, actively optimized LZMA/LZMA2 decoder that in our benchmarks
(21 MB LZMA1 stream) decodes roughly 1.4x faster than lzma-rs while
remaining 100% Rust.

Similarly, flate2's default rust_backend (miniz_oxide) is replaced with the
newer, faster zlib-rs backend for Compression=zlib installers.

Changes

• Cargo.toml: replace lzma-rs = "0.3.0" with
  lzma-rust2 = { version = "0.18", default-features = false, features = ["std", "optimization"] };
  switch flate2 to default-features = false, features = ["zlib-rs"].
  lzma-rs is kept as a dev-dependency only, because the chunk reader's
  tests still use lzma_rs::lzma_compress to build compressed fixtures.
• src/decompress/block.rs (decompress_inno_lzma1): decode with
  lzma_rust2::LzmaReader::new_mem_limit + std::io::copy instead of
  lzma_rs::lzma_decompress_with_options + UnpackedSize::UseProvided(None).
  Inno's non-standard 5-byte LZMA1 properties header is padded with the
  8-byte unknown-size sentinel (u64::MAX) to form the 13-byte LZMA-Alone
  header lzma-rust2 expects; the end-of-payload marker terminates the stream.
• src/extract/chunk.rs: same swap for decompress_lzma1, and the LZMA2
  branch now uses lzma_rust2::Lzma2Reader (32 MiB dictionary default; Inno's
  1-byte property prefix is skipped) + io::copy.

Behavior notes

• The decoder stops at the end-of-payload marker, so trailing bytes after the
  stream (CRC, padding) are left unread — the same data is produced as before.
• No changes to the public API; error mapping (Error::Decompress) is
  preserved.
• Verified against real-world installers (LZMA1 Compression=lzma/lzma2
  chunks, setup-0 blocks, solid chunks shared across files) with
  tree-identical extraction results, and the existing unit tests pass.

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