Set different timeouts for remappings in insert mode and in normal mode

Is your feature request related to a problem? Please describe.
Multi-key normal mode remappings have to be entered quickly because they share a timeout with insert mode remappings where it's desirable to have a shorter timeout.

Describe the solution you'd like
Allow setting a 2nd timeout that only applies either:

• only when in insert mode
• in modes other than insert mode

Describe alternatives you've considered
Alternatively allow setting a different timeout for every mode, but that may be overkill.

Additional context
I have implemented this feature already in a non-backwards compatible way, replacing configuration.timeout with configuration.insertModeTimeout and configuration.otherModesTimeout. Would be happy to get the change upstreamed in a backwards compatible way, let me know what your thoughts are.

EDIT: implementation https://github.com/reem/Vim/tree/split-timeouts

Start by reviewing the split-timeouts implementation linked in the issue and the existing timeout configuration and remapping handling. Done means supporting separate insert-mode and other-mode timeouts while preserving backward compatibility; add or update relevant tests if the implementation identifies them.