Added support to write Avro async

[jorgecarleitao]

This PR complets another milestone: both sync and async support to Avro.

The PR itself is quite simple since most of the operations are already available to us on the sync side of things.

[codecov]

Codecov Report

Merging #736 (a698ea4) into main (e001ba5) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #736      +/-   ##
==========================================
+ Coverage   70.76%   70.79%   +0.03%     
==========================================
  Files         311      313       +2     
  Lines       16879    16899      +20     
==========================================
+ Hits        11944    11964      +20     
  Misses       4935     4935              

Impacted Files	Coverage Δ
src/io/avro/mod.rs	66.66% <ø> (ø)
src/io/avro/write/mod.rs	91.66% <100.00%> (+0.75%)	⬆️
src/io/avro/write_async/block.rs	100.00% <100.00%> (ø)
src/io/avro/write_async/mod.rs	100.00% <100.00%> (ø)

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