fix: keep plugin flow timeline visible when the calls table overflows

[SaKaNa-Y]

Description

Fixed an issue where the left timeline was almost invisible when the window width was small.

before:

now:

Linked Issues

Additional context

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commit: 5bbb40f

[SaKaNa-Y]

I noticed that the left timeline cannot be scrolled when the window height is limited. I didn't change this behavior in this PR because I'm not sure whether scrolling is expected here.