feat: add infer and tree_magic_mini meta plugins, make zstd internal by default

- Add infer crate as meta plugin for MIME type detection
- Add tree_magic_mini crate as alternative meta plugin for MIME type detection
- Add zstd, infer, tree_magic_mini to default features
- Fix static build script to use musl target instead of glibc+crt-static
- Remove hardcoded shell list from --generate-completion help text
- Fix update() in both new plugins to emit MIME metadata when buffer fills

build-static.bash

@@ -2,7 +2,6 @@
 
 set -ex
 
-export RUSTFLAGS='-C target-feature=+crt-static'
-cargo build --release --target x86_64-unknown-linux-gnu
+cargo build --release --target x86_64-unknown-linux-musl
 mkdir -p bin
-cp target/x86_64-unknown-linux-gnu/release/keep ./bin/
+cp target/x86_64-unknown-linux-musl/release/keep ./bin/