feat: primary selection threshold

[Rational-Curiosity]

The primary_threshold_ms variable defines the time interval, in milliseconds, that controls how often the program updates its stored value of the Linux primary selection. In the Linux environment, the primary selection is a mechanism that automatically updates to reflect the current highlighted text or object, typically updating with every mouse movement.

[xrelkd]

Hi @Rational-Curiosity, thanks for the contribution.
To fit the conventional commit, I split the single commit into multiple commits and marked you as the co-author.
The PR is available here: #431 .
The primary_threshold_ms option is also set as 5000 by default since this feature is very useful!!!!!!