fix(components): [data-picker] use renderSlot simplified code

[FrontEndDog]

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Description

Similar to #14939

🤖[deprecated] Generated by Copilot at 2a206e7

Simplify slot rendering in BasicCellRender component. Use renderSlot function from vue to avoid manual slot checking and rendering in packages/components/date-picker/src/date-picker-com/basic-cell-render.tsx.

Related Issue

Fixes #___.

Explanation of Changes

🤖[deprecated] Generated by Copilot at 2a206e7

• Simplify the rendering of the default slot in the BasicCellRender component by using the renderSlot function from vue (link, link)

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