Replace specific functions with `mu4e-user-agent` properties #853

Job	Run time
check (ubuntu-latest, 26.3, false)	50s
check (ubuntu-latest, 27.2, false)	52s
check (ubuntu-latest, 28.2, false)	1m 8s
check (ubuntu-latest, 29.3, false)	1m 6s
check (macos-latest, 26.3, false)	51s
check (macos-latest, 27.2, false)	1m 3s
check (macos-latest, 28.2, false)	2m 21s
check (macos-latest, 29.3, false)	2m 25s
check (windows-latest, 26.3, false)	3m 30s
check (windows-latest, 27.2, false)	2m 22s
check (windows-latest, 28.2, false)	2m 36s
check (windows-latest, 29.3, false)	2m 22s
check (ubuntu-latest, snapshot, true)	47s
check (macos-latest, snapshot, true)	2m 8s
	24m 21s

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