Do not check offsets or utf8 validity in ffi (#505)

[NilsBarlaug]

As declared in the spec, the purpose of FFI is to be a very low cost API. The method is already intrinsically unsafe because the data must already follow the spec.

Changed Utf8Array::try_from_ffi and BinaryArray::try_from_ffi to use from_data_unchecked instead of from_data.

[codecov]

Codecov Report

Merging #510 (5ef1920) into main (8a7f1d7) will increase coverage by 0.00%.
The diff coverage is 87.50%.

@@           Coverage Diff           @@
##             main     #510   +/-   ##
=======================================
  Coverage   80.17%   80.18%           
=======================================
  Files         381      381           
  Lines       23659    23665    +6     
=======================================
+ Hits        18969    18975    +6     
  Misses       4690     4690           

Impacted Files	Coverage Δ
src/array/binary/mod.rs	78.75% <83.33%> (+0.37%)	⬆️
src/array/binary/ffi.rs	84.61% <100.00%> (ø)
src/array/utf8/ffi.rs	77.77% <100.00%> (ø)
src/io/ipc/write/common.rs	76.28% <0.00%> (+0.64%)	⬆️

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