GODT-1523: Reduce unnecessary shell executions. Inspired by @kortschak.

- check opened file descriptors
- detection of darwin version
- detection of apple interface color theme
- test for update sync (copy files)
- replace exec with execabs

internal/store/ulimit_windows.go

@@ -0,0 +1,23 @@
+// Copyright (c) 2022 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
+
+//go:build windows
+// +build windows
+
+package store
+
+func isFdCloseToULimit() bool { return false }