Legal holds, step 1: the hold itself

inbuxa:LegalHold get/set places a hold on accounts, groups, domains,
tenants or the whole server, with an optional date range. A hold's range
and scope can only widen, a released hold is read-only, and none is ever
deleted. Placing, changing and releasing each need a reason and are
audited (LH-1, LH-3, LH-10, AU-12).

Permissions 669-672 (see, place, widen or release, export held data)
go to server administrators only; the tenant ceiling always strips them,
as it does Impersonate (LH-13). Schema: Compliance > Legal Holds.

What a hold keeps comes next, through the undelete hooks.

Also moves the lock expiry helpers below the lock module's imports.

crates/jmap-proto/src/request/parser.rs

@@ -566,6 +566,21 @@ impl<'de> Visitor<'de> for CallVisitor {
                     return Err(de::Error::invalid_length(1, &self));
                 }
             },
+            // inbuxa: legal hold
+            (MethodFunction::Get, MethodObject::LegalHold) => match seq.next_element() {
+                Ok(Some(value)) => RequestMethod::Get(GetRequestMethod::LegalHold(value)),
+                Err(err) => RequestMethod::invalid(err),
+                Ok(None) => {
+                    return Err(de::Error::invalid_length(1, &self));
+                }
+            },
+            (MethodFunction::Set, MethodObject::LegalHold) => match seq.next_element() {
+                Ok(Some(value)) => RequestMethod::Set(SetRequestMethod::LegalHold(value)),
+                Err(err) => RequestMethod::invalid(err),
+                Ok(None) => {
+                    return Err(de::Error::invalid_length(1, &self));
+                }
+            },
             // inbuxa: the audit log
             (MethodFunction::Get, MethodObject::AuditEvent) => match seq.next_element() {
                 Ok(Some(value)) => RequestMethod::Get(GetRequestMethod::AuditEvent(value)),