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/request/mod.rs

@@ -117,6 +117,7 @@ pub enum GetRequestMethod {
     DeletedAccount(Box<GetRequest<crate::object::inbuxa_deleted_account::DeletedAccount>>),
     AiLimits(Box<GetRequest<crate::object::inbuxa_ai_limits::AiLimits>>),
     LogSettings(Box<GetRequest<crate::object::inbuxa_log_settings::LogSettings>>),
+    DlpSettings(Box<GetRequest<crate::object::inbuxa_dlp_settings::DlpSettings>>),
     DataInventory(Box<GetRequest<crate::object::inbuxa_data_inventory::DataInventory>>),
     InventorySnapshot(Box<GetRequest<crate::object::inbuxa_inventory_snapshot::InventorySnapshot>>),
     AuditEvent(Box<GetRequest<crate::object::inbuxa_audit::AuditEvent>>),
@@ -154,6 +155,7 @@ pub enum SetRequestMethod<'x> {
     DeletedAccount(Box<SetRequest<'x, crate::object::inbuxa_deleted_account::DeletedAccount>>),
     AiLimits(Box<SetRequest<'x, crate::object::inbuxa_ai_limits::AiLimits>>),
     LogSettings(Box<SetRequest<'x, crate::object::inbuxa_log_settings::LogSettings>>),
+    DlpSettings(Box<SetRequest<'x, crate::object::inbuxa_dlp_settings::DlpSettings>>),
     Explanation(Box<SetRequest<'x, crate::object::inbuxa_explanation::Explanation>>),
     AuditSettings(Box<SetRequest<'x, crate::object::inbuxa_audit::AuditSettings>>),
     AuditExport(Box<SetRequest<'x, crate::object::inbuxa_audit::AuditExport>>),