fix(axis): refactor axisLabel formatter

[Ovilia]

https://github.com/apache/echarts/pull/21220/changes#r2622525473

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Refactor to remove the indexOf call.

Fixed issues

Details

Before: What was the problem?

indexOf should not be necessary.

After: How does it behave after the fixing?

Use the index from map function`.

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

Security Checking

• This PR uses security-sensitive Web APIs.

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

N.A.

Merging options

• Please squash the commits into a single one when merging.

Other information

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[Copilot]

Pull request overview

This PR refactors the createAxisLabels function to eliminate an unnecessary indexOf call within a map operation. The change improves both code clarity and performance by utilizing the index parameter that map already provides.

Key Changes:

• Removed redundant indexOf call that was performing O(n) lookup on each map iteration
• Added index parameter to the map callback function to directly access the iteration index

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[github-actions]

The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-21432@921496a

[echarts-bot]

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