feat: add binary string operations (length and concatenation)

[f4t4nt]

This PR implements core binary string operations in Daft, supporting both regular binary and fixed-size binary types.

New Features

Binary String Operations

• Implemented core binary string methods:
  • binary.length(): Returns length of binary data
  • binary.concat(): Concatenates two binary arrays
  • binary.substr(): Extracts substring with optional length parameter

Fixed-Size Binary Support

• Extended all operations to work with fixed-size binary arrays:
  • Length operations return constant size
  • Concat preserves fixed-size semantics when concatenating two fixed-size arrays
  • For substr, fixed-size binaries are cast to regular binaries

[codspeed-hq]

CodSpeed Performance Report

Merging #3646 will degrade performances by 40.19%

_{Comparing nishant-binary-string (a973300) with main (e7abec3)}

Summary

❌ 1 regressions
✅ 26 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	nishant-binary-string	Change
❌	test_iter_rows_first_row[100 Small Files]	164.2 ms	274.6 ms	-40.19%

[kevinzwang]

Looks great so far!

[codecov]

Codecov Report

Attention: Patch coverage is 86.50794% with 51 lines in your changes missing coverage. Please review.

Project coverage is 77.93%. Comparing base (39bb62c) to head (a973300).
Report is 36 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	83.78%	12 Missing ⚠️
src/daft-core/src/array/ops/binary.rs	95.31%	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%   77.93%   -0.06%     
==========================================
  Files         720      726       +6     
  Lines       88794    90801    +2007     
==========================================
+ Hits        69252    70767    +1515     
- Misses      19542    20034     +492     

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	95.31% <95.31%> (ø)
src/daft-functions/src/binary/concat.rs	83.78% <83.78%> (ø)
src/daft-functions/src/binary/slice.rs	67.34% <67.34%> (ø)

... and 328 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.

[kevinzwang]

Looks good, feel free to merge once these last few comments are addressed