fix(marker): respect markLine z2 when computing label z2 in traverseUpdateZ (Fixes #21650)

[waterWang]

Brief Information

This pull request is in the type of:

• bug fixing

What does this PR do?

When the user sets a z2 value on a markLine, the label's z2 should reflect this value so the label stacks correctly relative to other series elements.

Root cause

traverseUpdateZ uses -Infinity as the initial maxZ2 value, and the label's z2 is computed as maxZ2 + 2 from child elements. If the child elements' z2 is not set (or set to 0) before traverseUpdateZ runs, the label gets a default z2 of 2, regardless of the markLine's z2 setting.

Fix

1. src/util/graphic.ts: Added an optional modelZ2 parameter to traverseUpdateZ(). When provided, it seeds the maxZ2 starting value, ensuring the label's z2 is at least modelZ2 + 2.

2. src/component/marker/MarkerView.ts: The updateZ function now reads the marker model's z2 value and passes it to traverseUpdateZ().

Fixed issues

• Fixes [Bug] Markline z2 is not effect on label #21650: Markline z2 is not effect on label

Before: What was the problem?

Setting markLine.z2 had no effect on the label's z-order. The label would always render at a default z2 level regardless of the markLine's z2 configuration.

After: How does it fix the problem?

The label's z2 now respects the markLine's z2 setting. The label's z2 is computed as max(modelZ2, childZ2) + 2, ensuring the label is always above the markLine elements and respects the user's z2 configuration.

Other information

This is a minimal fix that only affects the marker (markLine/markPoint/markArea) components. The traverseUpdateZ function's existing behavior is preserved for all other callers (the modelZ2 parameter is optional).

[echarts-bot]

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