Remove the @types/plotly.js dev dependency - #5759

Link to issue

Closes #5740

Description of change

Drops the @types/plotly.js dev dependency from js/. plotly.js ships its own declarations since 4.0 ("types": "./lib/index.d.ts"), and TypeScript prefers a package's bundled types over DefinitelyTyped, so the DT package was already unused: tsc resolved plotly.js to the bundled types all along, and Plotly.PlotlyHTMLElement only kept working through the export as namespace Plotly UMD declaration.

While at it, the type usage is made explicit against the bundled declarations:

• widget.ts imports PlotlyHTMLElement and uses a small PlotlyGraphDiv type for what plotly.js doesn't declare: _fullData/_fullLayout on the graph div and the plotly_update event. The plotly_deselect/plotly_doubleclick handlers take no argument now, matching the declared callback signature (they never used it).
• mimeExtension.ts had import type PlotlyType from "plotly.js" and then PlotlyType.Data etc. The default export is a value, not a namespace, so those never resolved. It is import type * as PlotlyType now, plus the same kind of local type for plotly_webglcontextlost.
• tsconfig.json: moduleResolution: "node" (node10) was removed in TypeScript 7, which package.json already pins (^7.0.2), so npm run typecheck failed before checking anything. Switched to bundler, which matches how esbuild consumes the sources.

Demo

npm run typecheck on main:

tsconfig.json(7,25): error TS5108: Option 'moduleResolution=node10' has been removed. Please remove it from your configuration.

Forcing --moduleResolution bundler on main gives 27 errors, 9 of them about plotly.js types: Cannot find namespace 'PlotlyType' (4×), No overload matches this call for plotly_update, plotly_deselect and plotly_doubleclick, and Property '_fullData' / '_fullLayout' does not exist on type 'PlotlyHTMLElement'. After this change it reports 18, all pre-existing and unrelated to plotly.js (implicit any, strict null checks, no declarations for lodash-es and @jupyterlab/rendermime-interfaces). I left those alone.

Testing strategy

No Python changes. Rebuilt with npm ci && npm run build after deleting plotly/labextension/: the labextension static bundle and js/lib/mimeExtension.js come out byte-identical (only types changed there), plotly/labextension/package.json picks up the dependency removal, and plotly/package_data/widgetbundle.js changes because of the two handler signatures (the rest of its diff is the minifier renaming identifiers). Type-checked as described above.

Additional information (optional)

No changelog entry, since this only touches the JS dev toolchain. Happy to add one if you prefer; otherwise the changelog check needs the no-changelog label.

Guidelines

• I have reviewed the pull request guidelines and the Code of Conduct and confirm that this PR follows them.
• I have added an entry to the changelog if needed (not required for documentation PRs).