Description
After upgrading from ngx-echarts 19.0.0 to 20.0.0, applying custom ECharts themes no longer works.
The charts display, but the theme colors and styles are not applied.
Reverting back to 19.0.0 fixes the problem.

Steps to reproduce

• Use ngx-echarts 20.0.0 in an Angular project.

• Register and apply a custom theme

• Render a chart and observe that the theme styles/colors are ignored.

• Downgrade to ngx-echarts 19.0.0 and the theme works as expected.

Expected behavior
Custom themes should be correctly applied to charts in ngx-echarts 20.0.0.

Screenshots or example

The official ngx-echarts demo page shows the same issue in version 20.0.0:
https://xieziyu.github.io/ngx-echarts/#/basic/basic-usage

Environment:

• Angular version: 20.0.4

• ngx-echarts version: 20.0.0

• ECharts version: 5.6.0

• Browser: Chrome

Additional context
I have verified the same theme works correctly in 19.0.0, so this seems to be a regression or breaking change in 20.0.0.
Would appreciate help fixing this.