Add pause/resume for locked voice message recording

[bmaximuml]

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• My commits are rebased on the latest main branch
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• Requires device testing with microphone access (not testable in this environment)

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Description

Adds a Pause button to the locked voice message recording UI (the state entered after swiping up on the mic button). Requested by the community: https://community.signalusers.org/t/pause-while-recording-voice-message/3357

How it works:

• After locking a recording, a "Pause" button appears alongside the existing "Cancel" button
• Tapping Pause freezes the duration timer and pauses the AVAudioRecorder; the button label switches to "Resume"
• Tapping Resume continues recording from the same point; the timer resumes from the correct elapsed time
• The Send button remains active in both locked and paused states
• Device sleep blocking is released on pause and re-acquired on resume

Implementation notes:

• AVAudioRecorder.pause() / .record() handle the audio layer natively; no audio segments need to be stitched together
• AVAudioRecorder.currentTime correctly excludes paused periods, so the minimum-duration check and final file duration are accurate
• The UI timer is stopped while paused; on resume voiceMemoPausedDuration is used to offset the elapsed-time calculation so the label picks up exactly where it left off
• New .recordingPaused case added to VoiceMemoRecordingState; all existing gesture-handler switch statements updated accordingly

Files changed:

• VoiceMessageInProgressDraft — isPaused, pauseRecording(), resumeRecording()
• ConversationInputToolbar — .recordingPaused state, Pause/Resume button in lockVoiceMemoUI(), timer helpers, adjusted duration label
• ConversationViewController+VoiceMessage — pauseRecordingVoiceMessage(), resumeRecordingVoiceMessage()
• ConversationViewController+ConversationInputToolbarDelegate — voiceMemoGestureDidPause(), voiceMemoGestureDidResume()
• Localizable.strings — 4 new strings (Pause, Resume + accessibility labels)
• VoiceMessageInProgressDraftTest — unit tests for initial state and stop-before-start safety

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