[MOD-13853] revert adding `TieredHNSWDiskParams::ThrottleCB, Modify ThrottleCB return type to int

[meiravgri]

• Revert [MOD-13853] Add throttle control callback signature for disk tiered index #908 change in TieredHNSWDiskParams

• Modify ThrottleCB typedef to return int.

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Note

Medium Risk
Header/API-level changes can break downstream compilation and any code expecting the old ThrottleCB signature or the removed TieredHNSWDiskParams fields.

Overview
Changes the disk-tiered throttling callback typedef ThrottleCB to return int instead of void, enabling callers to signal success/failure.

Reverts TieredHNSWDiskParams to an effectively-empty struct by removing the enableThrottleCB/disableThrottleCB function pointers and replacing them with a placeholder field (with a note to potentially consolidate with TieredHNSWParams).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.09%. Comparing base (69bbc39) to head (4691dd1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #909      +/-   ##
==========================================
- Coverage   97.12%   97.09%   -0.03%     
==========================================
  Files         129      129              
  Lines        7500     7500              
==========================================
- Hits         7284     7282       -2     
- Misses        216      218       +2     

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