rust-compression: move the `Send` bound to the `Compressor` trait All compressors should be `Send`, might as well make any future use easier.

rust-inner-revlog: cache the compressor The `compress` function is unlikely to be used in highly contended situations, and creating a compressor has some overhead, on top of losing out on some potential advantages of longer-running optimizations from the compressor.

rust-lib: remove exports for not too common pattern-related types This only muddies the lib and makes the imports more confusing.

rust-lib: move `PatternError` to the `filepatterns` module This is where it belongs

rust-lib: move `Dirstate*Error` to the `dirstate` module That's where they belong and should always have been there.

rust-lib: only export very common types to the top of the crate This was done very early in the Rust project's lifecycle and I had very little Rust experience. Let's keep the `DirstateParents` since they'll pop up in all higher-level code and make the rest more explicit imports to make the imports less confusing and the lib less cluttered.

rust-dirstate: remove star exports This makes the crate's imports confusing and muddies the discovery of the code.