Added set_len method to Buffer

[haixuanTao]

Adding set_len enables to change the length value of the buffer.

This is required if get_mut changes the length of the buffer.

I think it will be great to add generic vector method such as extend_from_slice, copy_from_slice, with the according length change. I can add it to this pull request if interested.

[codecov]

Codecov Report

Base: 83.61% // Head: 83.67% // Increases project coverage by +0.06% 🎉

Coverage data is based on head (4a654f6) compared to base (615300b).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1374      +/-   ##
==========================================
+ Coverage   83.61%   83.67%   +0.06%     
==========================================
  Files         373      373              
  Lines       40326    40329       +3     
==========================================
+ Hits        33720    33747      +27     
+ Misses       6606     6582      -24     

Impacted Files	Coverage Δ
src/buffer/immutable.rs	86.66% <0.00%> (-2.55%)	⬇️
src/bitmap/utils/slice_iterator.rs	97.56% <0.00%> (-1.22%)	⬇️
src/array/utf8/mod.rs	83.98% <0.00%> (-1.18%)	⬇️
src/io/ipc/read/stream_async.rs	76.02% <0.00%> (-0.69%)	⬇️
src/offset.rs	86.11% <0.00%> (+0.34%)	⬆️
src/io/ipc/read/file_async.rs	72.76% <0.00%> (+11.56%)	⬆️

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[jorgecarleitao]

Thank you for the PR! 🙇 Indeed this is needed in some cases.

[jorgecarleitao]

Note that Buffer is primarily an immutable container (think Arc<Vec<>>), this is why we do not expose mutable methods to it (other than returning the mutable vector ^^)