fix: duplicate Y-axis labels when dynamic scale is enabled

[djbarnwal]

When the "Dynamic Y-axis scale" toggle is enabled and the data range is narrow, Y-axis tick labels can all show the same value (e.g., "$4k, $4k, $4k, $4k").

• Add formatUniqueTickLabels in utils.ts that formats ticks with the axis
  formatter first, then falls back to the table formatter (higher precision)
  if any labels are duplicated
• Pass pre-computed yTickLabels to MeasureChartGrid instead of the raw
  axisFormatter function

https://linear.app/rilldata/issue/APP-855/duplicate-axis-labels-in-measure-charts

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!