Add eventData handler to heatmap for proper click event data

[nojaf]

Fixes #7685

This PR adds an eventData handler to the heatmap trace module, enabling proper plotly_click event data with x, y, and z values.

Also fixes a bug in hover.js where category axis labels were incorrectly returning numeric boundary values instead of the actual category labels.

Changes:

• src/traces/heatmap/index.js - Register the eventData handler
• src/traces/heatmap/event_data.js - New file implementing the event data extraction
• src/traces/heatmap/hover.js - Fix category axis label lookup to use `xa._categories[nx]

[alexcjohnson]

Thanks @nojaf - your fix looks plausible, though I'm a little surprised this hasn't come up before. Can you make one or two standalone examples (in codepen preferably) that show the bugs this fixes? Then we can swap between using the latest release version and the build from your PR, which is available as a CI artifact here

[nojaf]

Hi @alexcjohnson,

I've been investigating further and I'm no longer sure the problem is in Plotly. It might be in the Marimo integration layer. I tried reproducing the issue with raw Plotly and react-plotly, but couldn't recreate what I see in Marimo notebooks.

I'll keep digging. If you don't hear from me within a week, feel free to close both the PR and the issue.