strip control characters from guest cloud-init log lines

[Nashit-h]

What This PR Changes

The hostagent reads cloud-init log lines from the guest over SSH and forwards them in CloudInitProgress events, which limactl start and limactl watch print to the operator's terminal with a bare %s. A guest controls those bytes (anything in /var/log/cloud-init-output.log or the cloud-init journald output), so it can emit ANSI/OSC escape sequences and spoof or rewrite the terminal during the default start progress display. This strips non-printable runes at the single emit choke point (emitCloudInitProgressEvent) so every consumer is safe, matching the removeControlChars handling already used for other guest-controlled strings and the %#q quoting used for the sibling guest-error path.

Linked Issue (Required in most cases)

Small self-contained security fix; no separate tracking issue.

How I Tested This

Added a regression test that runs an escape sequence through emitCloudInitProgressEvent and asserts the emitted LogLine has no control characters. It fails on the current code (the \x1b survives) and passes with this change. go test ./pkg/hostagent/... and the repo-pinned golangci-lint run ./pkg/hostagent/ are green.

AI Usage

[AkihiroSuda]

Duplicated code:

lima/pkg/cidata/cidata.go

Lines 499 to 507 in 20dbdc0

	func removeControlChars(s string) string {
	out := make([]rune, 0, len(s))
	for _, r := range s {
	if unicode.IsPrint(r) {
	out = append(out, r)
	}
	}
	return string(out)
	}

Should be moved to pkg/strutil

[Nashit-h]

Good point. Moved it to strutil.RemoveControlChars and switched both cidata and the hostagent path over to it.

[AkihiroSuda]

Please squash the commits