Improve interactive shell performance for pasted user input

[adfoster-r7]

Improves the interactive shell performance when reading user input.
Note that this functionality is behind a feature flag, enabled with:

features set fully_interactive_shells true

Before

When a user pastes the following input into their interactive shell -it:

echo 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 | base64 -d

The input is read a character at a time, and the user has to wait for the buffer to be read:

After

The user input is read 1024 characters at a time, and there's no longer any noticeable lag:

Verification

• Acquire a linux meterpreter shell
• Run shell -it
• Paste the input and verify it no longer lags

[adfoster-r7]

Unrelated to this PR, but also noticing that there's a call to handle a line of user input:

metasploit-framework/lib/rex/post/meterpreter/ui/console/interactive_channel.rb

Line 84 in 9574100

self.on_command_proc.call(data.strip) if self.on_command_proc

Which interactive shells may break the assumptions of

[dwelch-r7]

Release Notes

Improves interactive shell performance for pasted user input