feat: add binary string operations (length and concatenation)

[f4t4nt]

Added two new binary string operations to Daft:\n\n- binary.length(): Get length of binary strings in bytes\n- binary.concat(): Concatenate two binary strings\n\nImplemented in Rust with full test coverage including ASCII, UTF-8, and special binary sequences.

[codspeed-hq]

CodSpeed Performance Report

Merging #3646 will improve performances by 49.11%

_{Comparing nishant-binary-string (4e4b23f) with main (c650794)}

Summary

⚡ 1 improvements
✅ 26 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	nishant-binary-string	Change
⚡	test_show[100 Small Files]	23.6 ms	15.8 ms	+49.11%

[kevinzwang]

Looks great so far!

[codecov]

Codecov Report

Attention: Patch coverage is 86.82171% with 51 lines in your changes missing coverage. Please review.

Project coverage is 77.88%. Comparing base (39bb62c) to head (4e4b23f).
Report is 27 commits behind head on main.

Files with missing lines	Patch %	Lines
src/daft-functions/src/binary/slice.rs	67.34%	16 Missing ⚠️
src/daft-functions/src/binary/concat.rs	84.21%	12 Missing ⚠️
src/daft-core/src/array/ops/binary.rs	95.47%	9 Missing ⚠️
src/daft-core/src/series/ops/binary.rs	46.66%	8 Missing ⚠️
src/daft-functions/src/binary/length.rs	80.64%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3646      +/-   ##
==========================================
- Coverage   77.99%   77.88%   -0.11%     
==========================================
  Files         720      737      +17     
  Lines       88794    90984    +2190     
==========================================
+ Hits        69252    70866    +1614     
- Misses      19542    20118     +576     

Files with missing lines	Coverage Δ
daft/expressions/expressions.py	93.64% <100.00%> (+0.13%)	⬆️
src/daft-core/src/series/ops/mod.rs	100.00% <ø> (ø)
src/daft-functions/src/lib.rs	0.00% <ø> (ø)
src/daft-functions/src/python/mod.rs	100.00% <100.00%> (ø)
src/daft-functions/src/binary/length.rs	80.64% <80.64%> (ø)
src/daft-core/src/series/ops/binary.rs	46.66% <46.66%> (ø)
src/daft-core/src/array/ops/binary.rs	95.47% <95.47%> (ø)
src/daft-functions/src/binary/concat.rs	84.21% <84.21%> (ø)
src/daft-functions/src/binary/slice.rs	67.34% <67.34%> (ø)

... and 300 files with indirect coverage changes

[kevinzwang]

Looks good so far! In addition to the other comments there's two things you should also do:

• add these functions to our docs by adding a section in docs/source/api_docs/expressions.rst
• implement this for the FixedSizeBinaryArray type as well

[kevinzwang]

Looks good so far! I had some comments on things to clean up.