feat(embed): const constructors, output accessors and owned tables in flate

[MagicalTux]

What

Ports minizlib's last two commits into embed::flate. Without them, the minizlib 0.1.1 → re-export switch (KarpelesLab/minizlib#5) would lose API that minizlib's master has gained.

• const fn new on Decompressor and Compressor. Given an output and a table that start as all zeros, a new codec is all zeros too, so it can live in a static in .bss and costs no flash. The position where the stream starts is now read on first use, since a const fn can't ask the output for it.
• output() / output_mut() on both, so the caller can drain their own Output between pieces.
• Owned tables: Compressor<'t, O, F, T = &'t mut [u16]> accepts any T: AsMut<[u16]>, e.g. [0u16; 4096]. The default type parameter keeps existing code compiling.
• Shared checksums: adds Container::INIT. flate now uses embed's own CRC-32 and Adler-32, which start from all zeros like minizlib's do now, and drops its own copy.

After folding the feature gates the same way as in #135, the ported files are identical to minizlib's master, apart from removing dead branches.

Footprint

configuration	code	was	ceiling
Decompressor	3424	3460	3650
gzip, buffer out	1030	982	1050 → 1100
Compressor, streams	1404	1344	1450 → 1500
BufferedCompressor	1600	1522	1600 → 1700

No panic machinery is linked. The ceilings were raised to restore about 5% headroom.

Tests

New tests/embed_flate_embedding.rs, added to CI's embed test step:

• both codecs built in statics and reused;
• an owned table produces the same stream as a borrowed one;
• output drained between pieces.

These pass locally:

• fmt;
• clippy on --features all, --all-features, embed,gzip and embed;
• rustdoc with -D warnings;
• cargo test --all-features and the embed test step;
• the thumbv7em build;
• the MSRV 1.88 check;
• tools/footprint/check.sh.

🤖 Generated with Claude Code