refactor(gateway)!: rewrite Inflater

[vilgotf]

Removes the Inflater internal buffer and instead returns the decompressed (and now String) message directly. Note that this does not add any allocations since the old implementation took the buffer on each message (which also probably caused bugs when events were split across two compressed messages). The old implementation also faultily always returned None when decompression was disabled, making it impossible to process messages. There are also other smaller improvements caused by this rewrite.

Removes the Message::Binary variant since decompressed must now be Strings to be valid. Users should not have a problem being restricted to UTF-8 messages since the gateway only accepts JSON encoded events.

Removes the metrics feature and conditionally exposes the Inflater directly for users to use however they wish.

Fixes #1990

[Erk-]

The changes looks overall good

I am not really a fan of switching it to parse strings around for a couple of reasons

• It is less flexible in general for what you can do with them
• It makes some optimizations have less gain such as simd-json which does with simd accelerated checking of utf-8.