Add normalized OrderBy stream methods

[gordonwatts]

This just adds the methods, it does not implement them. However, they have to be here before they can be implemented. Once this PR is approved and merged, then the changes can go into the backends.

Summary

• Add OrderBy and OrderByDescending to ObjectStream with normalized backend-visible AST calls
• Preserve the key selector lambda in the query AST without performing local sorting
• Extend extension-function normalization coverage for the new operators

Validation

• .venv\Scripts\python.exe -m pytest tests/test_object_stream.py tests/ast/test_func_adl_ast_utils.py -q
• .venv\Scripts\python.exe -m black --check --target-version py313 tests/test_object_stream.py tests/ast/test_func_adl_ast_utils.py func_adl/object_stream.py func_adl/ast/func_adl_ast_utils.py
• .venv\Scripts\python.exe -m flake8 func_adl tests

Fixes #22

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.81%. Comparing base (bc64538) to head (3d0205a).
⚠️ Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #232      +/-   ##
==========================================
+ Coverage   95.72%   95.81%   +0.08%     
==========================================
  Files          15       15              
  Lines        1662     1672      +10     
==========================================
+ Hits         1591     1602      +11     
+ Misses         71       70       -1     

Flag	Coverage Δ
unittests	95.81% <100.00%> (+0.08%)	⬆️

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