DLP: how long held mail waits is a setting

inbuxa:DlpSettings (singleton, urn:inbuxa:jmap): keepHeldDays, 1 to 90,
7 by default (settled answer 5 made it a setting). sysDlpPolicyGet reads
it, sysDlpPolicyUpdate changes it, server-level, audited by the request
layer. Each held message keeps the days it was given, and the sender's
notices say that number. Privacy catalog entry; spec §2.6 updated.

mail_rules_tests: 7 by default, 0 refused, 3 set and a message held
afterwards expires 3 days after it was held, the expiry notice says 3.

crates/jmap-proto/src/response/mod.rs

@@ -104,6 +104,7 @@ pub enum GetResponseMethod {
     DeletedAccount(GetResponse<crate::object::inbuxa_deleted_account::DeletedAccount>),
     AiLimits(GetResponse<crate::object::inbuxa_ai_limits::AiLimits>),
     LogSettings(GetResponse<crate::object::inbuxa_log_settings::LogSettings>),
+    DlpSettings(GetResponse<crate::object::inbuxa_dlp_settings::DlpSettings>),
     DataInventory(GetResponse<crate::object::inbuxa_data_inventory::DataInventory>),
     InventorySnapshot(GetResponse<crate::object::inbuxa_inventory_snapshot::InventorySnapshot>),
     AuditEvent(GetResponse<crate::object::inbuxa_audit::AuditEvent>),
@@ -142,6 +143,7 @@ pub enum SetResponseMethod {
     DeletedAccount(Box<SetResponse<crate::object::inbuxa_deleted_account::DeletedAccount>>),
     AiLimits(Box<SetResponse<crate::object::inbuxa_ai_limits::AiLimits>>),
     LogSettings(Box<SetResponse<crate::object::inbuxa_log_settings::LogSettings>>),
+    DlpSettings(Box<SetResponse<crate::object::inbuxa_dlp_settings::DlpSettings>>),
     AuditSettings(Box<SetResponse<crate::object::inbuxa_audit::AuditSettings>>),
     AuditExport(Box<SetResponse<crate::object::inbuxa_audit::AuditExport>>),
     AuditVerification(Box<SetResponse<crate::object::inbuxa_audit::AuditVerification>>),
@@ -363,6 +365,12 @@ impl<'x> From<GetResponse<crate::object::inbuxa_log_settings::LogSettings>> for
     }
 }
 
+impl<'x> From<GetResponse<crate::object::inbuxa_dlp_settings::DlpSettings>> for ResponseMethod<'x> {
+    fn from(value: GetResponse<crate::object::inbuxa_dlp_settings::DlpSettings>) -> Self {
+        ResponseMethod::Get(GetResponseMethod::DlpSettings(value))
+    }
+}
+
 impl<'x> From<GetResponse<crate::object::inbuxa_data_inventory::DataInventory>> for ResponseMethod<'x> {
     fn from(value: GetResponse<crate::object::inbuxa_data_inventory::DataInventory>) -> Self {
         ResponseMethod::Get(GetResponseMethod::DataInventory(value))
@@ -387,6 +395,12 @@ impl<'x> From<SetResponse<crate::object::inbuxa_log_settings::LogSettings>> for
     }
 }
 
+impl<'x> From<SetResponse<crate::object::inbuxa_dlp_settings::DlpSettings>> for ResponseMethod<'x> {
+    fn from(value: SetResponse<crate::object::inbuxa_dlp_settings::DlpSettings>) -> Self {
+        ResponseMethod::Set(SetResponseMethod::DlpSettings(Box::new(value)))
+    }
+}
+
 impl<'x> From<SetResponse<crate::object::inbuxa_explanation::Explanation>> for ResponseMethod<'x> {
     fn from(value: SetResponse<crate::object::inbuxa_explanation::Explanation>) -> Self {
         ResponseMethod::Set(SetResponseMethod::Explanation(Box::new(value)))