feat: DH-18779: Auto-resize column header groups

[vbabich]

• Calculate adjusted paddings for columns based on the width of column header groups. Pre-requisite for DH-18780
• Add optional getMetricCalculator prop in IrisGrid and IrisGridPanel, needed to override metric calculator for Pivots
  Fix duplicated mouseHanders prop in the handlers array in IrisGrid

[codecov]

Codecov Report

❌ Patch coverage is 44.55446% with 56 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.91%. Comparing base (35b3bf2) to head (71e02fb).

Files with missing lines	Patch %	Lines
packages/iris-grid/src/IrisGridMetricCalculator.ts	20.00%	56 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2566      +/-   ##
==========================================
+ Coverage   44.27%   44.91%   +0.63%     
==========================================
  Files         768      769       +1     
  Lines       43367    43466      +99     
  Branches    11154    11173      +19     
==========================================
+ Hits        19202    19524     +322     
+ Misses      24118    23926     -192     
+ Partials       47       16      -31     

Flag	Coverage Δ
unit	44.91% <44.55%> (+0.63%)	⬆️

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[Copilot]

Pull Request Overview

This PR adds tree rebalancing functionality for column header groups in IrisGrid, enabling proper width distribution across hierarchical header structures.

• Introduces a new TreeRebalanceUtil module with rebalancing algorithm
• Integrates tree rebalancing into IrisGridMetricCalculator for column header padding calculations
• Adds getMetricCalculator prop to allow custom metric calculator injection

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
TreeRebalanceUtil.ts	New module implementing tree rebalancing algorithm for distributing values across hierarchical structures
TreeRebalanceUtil.test.ts	Comprehensive test suite for tree rebalancing functionality
IrisGridMetricCalculator.ts	Integrates tree rebalancing for column header group width calculations with caching
IrisGridMetricCalculator.test.ts	Adds missing mock for columnHeaderGroups property
IrisGrid.tsx	Adds getMetricCalculator prop and removes mouseHandlersProp destructuring
IrisGridPanel.tsx	Passes through getMetricCalculator prop to IrisGrid

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