[BUG] Support "NONE" string value for max-error-lines in TOML config

[d-biehl]

Support Robot Framework's NONE value for max-error-lines in TOML config

Description

max-error-lines maps to Robot Framework's --maxerrorlines CLI argument.

Robot Framework allows the special value NONE for this option:

robot --maxerrorlines NONE

This is useful when the full error output should be shown without limiting it to a fixed number of lines.

However, it is currently unclear how to configure this value in RobotCode's TOML configuration.

Using None is not valid TOML:

max-error-lines = None

The TOML-compatible representation would be a string:

max-error-lines = "NONE"

Expected behavior

RobotCode should allow configuring Robot Framework's special NONE value through TOML, for example:

max-error-lines = "NONE"

and pass it to Robot Framework as:

--maxerrorlines NONE

Actual behavior

max-error-lines appears to be documented/validated as int | None.

Since TOML has no None value, this makes it unclear how to configure Robot Framework's supported NONE value from a TOML config file.

Suggested solution

Allow "NONE" as a valid value for max-error-lines, or document the intended TOML representation for Robot Framework's --maxerrorlines NONE.

Originally posted by @ngblume in #385