fix(explore): stop metric edits from bleeding across metrics with duplicate optionNames

[jesperct]

SUMMARY

Editing one custom (adhoc) metric could silently rewrite other metrics on the same chart. When a chart's saved metrics include two adhoc metrics that share an optionName (which can happen, for example after duplicating a metric), editing one of them overwrote every metric with that optionName — both the label and the definition snapped to the edited one.

Root cause: the metric controls match an edit back to its metric by optionName, but nothing guaranteed optionName was unique. This fixes it where metrics are loaded into the control (coerceMetrics / coerceAdhocMetrics): a metric whose optionName collides with an earlier one is given a fresh optionName, so each metric keeps a unique identity. That both heals already-affected saved charts and prevents the behavior going forward. The fix is applied to the drag-and-drop metric control used by Explore and to the legacy metrics control, which share the same matching logic.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

Before: editing one metric's aggregate (SUM → MAX) also changes the second metric, leaving two identical MAX(num) metrics.
After: only the edited metric changes; the second metric stays AVG(num).

TESTING INSTRUCTIONS

1. Open a chart whose form_data holds two adhoc metrics on the same column that share an optionName (this is the state a duplicated metric can leave behind).
2. Edit one metric (e.g. change its aggregate or label) and save.
   • Before: both metrics change together.
   • After: only the edited metric changes; the other is untouched.
3. Unit coverage: DndMetricSelect.test.tsx and MetricsControl.test.tsx assert that loading two metrics with a duplicate optionName yields unique identities so an edit touches only one.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
• Introduces new feature or API
• Removes existing feature or API

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[codecov]

Codecov Report

❌ Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 64.33%. Comparing base (c218dc4) to head (ef0e30b).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
...ontrols/DndColumnSelectControl/DndMetricSelect.tsx	90.90%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #41208   +/-   ##
=======================================
  Coverage   64.33%   64.33%           
=======================================
  Files        2651     2651           
  Lines      144766   144779   +13     
  Branches    33401    33405    +4     
=======================================
+ Hits        93131    93145   +14     
+ Misses      49965    49964    -1     
  Partials     1670     1670           

Flag	Coverage Δ
javascript	68.49% <94.11%> (+<0.01%)	⬆️

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