Attempt to safetly prevent duplicated execution commandline

[anthonykim1]

Co-authored-by: Daniel Imms @Tyriar

[anthonykim1]

To prevent duplicated Terminal REPL execution commandLine (...venv/bin/python etc) and python command, we may still have to await on exitCode for python to return undefined after it has launched REPL in terminal and/or increase timeout of checking for terminal.shellIntegration from 0.5 to longer (Should check settings as the biggest signal, and past terminals as a secondary signal in this case).

[anthonykim1]

Will handle fix for Keyboard Interrupt in separate PR: mainly from 2044f83