feat: add AbstractCommand::callSilently()

[paulbalandan]

Description
Extracted from michalsn's review on #10174.

Adds AbstractCommand::callSilently($command, $arguments, $options, $noInteractionOverride = true) to invoke another modern command with its output discarded, so the parent can emit its own consolidated message.

Supporting pieces:

• CodeIgniter\CLI\NullInputOutput — an InputOutput sink that discards writes and returns an empty string from input().
• CLI::getInputOutput() (@internal) — getter symmetric to the existing setInputOutput() / resetInputOutput() pair.
• CLI::getLastWrite() / CLI::setLastWrite() (@internal) — snapshot-and-restore accessors for $lastWrite so the silenced sub-command's writes don't leak the "suppress leading newline" state into the parent's next output.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Thanks!