Fixed error writing dictionary extension to IPC

[jorgecarleitao]

Dictionary extensions are tricky in that they are represented by a single Field in IPC, but are represented as Dictionary(Extension()) as a DataType, which requires some custom code to handle correctly. This PR does this

[codecov]

Codecov Report

Merging #397 (30bada9) into main (f326fed) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #397   +/-   ##
=======================================
  Coverage   81.13%   81.13%           
=======================================
  Files         347      347           
  Lines       21991    21996    +5     
=======================================
+ Hits        17842    17847    +5     
  Misses       4149     4149           

Impacted Files	Coverage Δ
src/io/ipc/convert.rs	94.95% <100.00%> (+0.04%)	⬆️
tests/it/io/ipc/write/file.rs	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f326fed...30bada9. Read the comment docs.