[CJstate]

Why is this change needed?

A markPoint data item positioned by a plain coord array (no statistic type, no explicit value field) reaches the label formatter with params.value === undefined, so {c} renders as undefined. This is most visible with a time base axis, where users naturally write coord: ['2024-01-02', 200] and expect the marker label to show the value at that point. close #20410

Root cause

dataTransform only assigns item.value for statistic types (max/min/average/median). For a plain coord item, the marker's SeriesData stores the raw option object {coord: [...]}, and MarkerModel.getDataParams builds params.value via retrieveRawValue(mpData, idx) without a dimension — which returns the raw option object's value field, i.e. undefined. The type: 'max' path works because line 143 forces item.value = coordInfo[1].

What does this PR do?

In dataTransform (src/component/marker/markerHelper.ts), when the coord branch finishes and item.value == null:

1. Resolve base/value axes via the existing getAxisInfo.
2. Parse the base-dimension coord through axisInfo.baseAxis.scale.parse(...) — this is what makes a time axis work, where coord[0] is a date string that must become a timestamp before lookup.
3. Find the nearest host-series datum with seriesModel.indicesOfNearest(...) and copy its value-dimension value into item.value.

The marker label and tooltip then carry the actual data value at that coord, consistent with what type: 'max' already produces. markLine and markArea share dataTransform, so coord-only items there get the same benefit.

How is it tested?

New unit test test/ut/spec/component/marker/markPointCoord.test.ts:

• formatter_params_carry_the_value_for_a_coord_markPoint_on_a_time_axis — captures the formatter params for the exact issue repro (time axis, coord-only item) and asserts params.value is defined. Fails on master, passes with this fix.
• defaultedLabel_dims_carry_the_value_for_coord_markPoint — guards the default-label dim path.

Full local suite: npx jest --config test/ut/jest.config.cjs → 27 suites / 196 tests passed, no regressions. npm run checktype reports no errors in the touched files.

What cannot be tested locally?

The sandbox cannot run the full browser rendering pipeline (npm run dev visual cases), but the change only touches data-transform logic that the Jest suite covers.

close #20410

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