Initial implementation of arca, a LUKS volume manager.

Go CLI using cobra with mount, unmount, status, and init subcommands.
Unlocks via udisks2 D-Bus (passphrase/keyfile) or cryptsetup (FIDO2/TPM2)
with ordered method fallback. Includes NixOS-specific LD_LIBRARY_PATH
injection for systemd cryptsetup token plugins.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/godbus/dbus/v5/sequence.go

@@ -0,0 +1,24 @@
+package dbus
+
+// Sequence represents the value of a monotonically increasing counter.
+type Sequence uint64
+
+const (
+	// NoSequence indicates the absence of a sequence value.
+	NoSequence Sequence = 0
+)
+
+// sequenceGenerator represents a monotonically increasing counter.
+type sequenceGenerator struct {
+	nextSequence Sequence
+}
+
+func (generator *sequenceGenerator) next() Sequence {
+	result := generator.nextSequence
+	generator.nextSequence++
+	return result
+}
+
+func newSequenceGenerator() *sequenceGenerator {
+	return &sequenceGenerator{nextSequence: 1}
+}