feat(env_var): Add support for env_var.VAR in format

[davidkna]

Description

This PR allows using ${env_var.VAR} in format strings. Unlike #3375, I handled this in a shared manner with custom modules by moving the code paths for custom and env_var modules closer to other regular modules, leveraging modules::handle (which tests for custom modules were using). This allows removing the timing-handling from the custom module code.

Motivation and Context

Closes #3259
Closes #3375

Screenshots (if appropriate):

How Has This Been Tested?

• I have tested using MacOS
• I have tested using Linux
• I have tested using Windows

Checklist:

• I have updated the documentation accordingly.
• I have updated the tests accordingly.

[andytom]

LGTM but looks like we have some merge conflicts.

[jaimehrubiks]

for some reason I cannot make this work

right_format = """>${env_var.ZVM_MODE_CUSTOM}<"""
[env_var.ZVM_MODE_CUSTOM]
variable = 'ZVM_MODE_CUSTOM'
default = ''

[davidkna]

@jaimehrubiks These changes aren't included in the latest version of starship yet. They will be included with starship v1.13.

[jaimehrubiks]

Ups, now I see! Thank you!