perf: lazily import pyiceberg and unity catalog if available

[jaychia]

memray reports that a not-insignificant amount of memory is being taken by our catalog module at import-time

This PR makes those imports lazy

[codspeed-hq]

CodSpeed Performance Report

Merging #3565 will degrade performances by 27.38%

_{Comparing jay/lazy-imports-catalogs (9b964b5) with main (35ed63c)}

Summary

⚡ 1 improvements
❌ 2 regressions
✅ 24 untouched benchmarks

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

Benchmarks breakdown

	Benchmark	main	jay/lazy-imports-catalogs	Change
❌	test_count[1 Small File]	3.3 ms	4 ms	-17.14%
❌	test_iter_rows_first_row[100 Small Files]	175.2 ms	241.2 ms	-27.38%
⚡	test_show[100 Small Files]	19 ms	15.9 ms	+19.48%

[codecov]

Codecov Report

Attention: Patch coverage is 13.33333% with 13 lines in your changes missing coverage. Please review.

Project coverage is 77.79%. Comparing base (35ed63c) to head (9b964b5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
daft/catalog/__init__.py	13.33%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3565      +/-   ##
==========================================
- Coverage   77.81%   77.79%   -0.02%     
==========================================
  Files         716      716              
  Lines       87987    87991       +4     
==========================================
- Hits        68463    68455       -8     
- Misses      19524    19536      +12     

Files with missing lines	Coverage Δ
daft/catalog/__init__.py	30.55% <13.33%> (-25.70%)	⬇️

... and 1 file with indirect coverage changes