WOR-1487: expose workflow instance location hints

[Caio-Nogueira]

Add the location hint option to the public and internal Workflow instance creation declarations.

[ask-bonk]

The apac-ne/apac-se sub-regions come from the generated RTTI for DurableObjectLocationHint (C++ source), not from defines/. This is a separate type defined in C++, so the difference is by design -- the Workflow type is a separate hand-written definition.

This PR looks clean. The changes are:

1. Purely additive (new optional type + optional field)
2. Backward-compatible
3. Consistent across all 6 files
4. No security concerns (type declarations only)
5. No behavioral changes requiring compat flags

LGTM

github run

[codspeed-hq]

Merging this PR will not alter performance

✅ 72 untouched benchmarks
⏩ 129 skipped benchmarks¹

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_{Comparing WOR-1487 (dfec943) with main (343766b)}

Footnotes

1. 129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.48%. Comparing base (d900d79) to head (dfec943).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6961      +/-   ##
==========================================
- Coverage   68.52%   68.48%   -0.04%     
==========================================
  Files         438      438              
  Lines      130004   130176     +172     
  Branches    21404    21424      +20     
==========================================
+ Hits        89079    89150      +71     
- Misses      27900    27987      +87     
- Partials    13025    13039      +14     

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