Add gzip and blosc decoders

[manzt]

Not sure if this would be on interest to the project, but I added support for gzip and blosc compression. Also added new fixtures and tests for the supported codecs.

[manzt]

The codecs can be expensive to load upfront, so an option is to make codecs load dynamically:

let blosc
let pako
const decoders = new Map()
   .set('zlib', async c => {
     if (!pako) pako = require('pako')
     return pako.inflate(c)
   })
   .set('gzip', async c => {
     if (!pako) pako = require('pako')
     return pako.ungzip(c)
   })
   .set('blosc', async c => {
     if (!blosc) {
       const Blosc = require('numcodecs/blosc')
       blosc = new Blosc()
     }
     return blosc.decode(c)
   })