make cursor_trail work on the same command prompt only

[xuhdev]

Is your feature request related to a problem? Please describe.

Currently cursor_trail always shows cursor movement once the distance is beyond a certain threshold.

However, in most cases when the cursor makes a big movement, my eyes either know where
it will land or don't care. For example,

• After typing in a long command and pressing "Enter", I know it will show up in the next command line prompt.
• When a program outputs long segments of text, I don't care where the cursor is.

However, the unnecessary animation in these scenarios is distractive.

The moments I see cursor_trail is only needed when I move cursor within a prompt
buffer. For example, I may press Alt-F to jump a word, and the word has an
unknown length to my eyes until I look carefully.

I tried to adjust cursor_trail_start_threshold and cursor_trail_decay, but
they don't seem to be able to address the problem.

Describe the solution you'd like
Add a new option cursor_trail_scenario to specify when to enable cursor
movement.

[wwqwq2313]

Hello, we tried to solve the issue.

This is what we did:

Added a new cursor_trail_scenario option to control when the cursor trail is shown. Updated the cursor trail logic to check this option before rendering.

You can review changes in this commit: wwqwq2313@3f6821e.

Caution

Disclaimer: The concept of solution was created by AI and you should never copy paste this code before you check the correctness of generated code. Solution might not be complete, you should use this code as an inspiration only.

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[kovidgoyal]

@jinhwanlazy please review.