Add ability to hold entries back from sequencing to reduce partial tiles

Add parameter specifying the maximum number of times a pending entry
might be held back to prefer creating full tiles instead of partial
tiles. fixes #33

This change required moving the logic to load the SequenceState from the
sequence_entries function to the wrapping sequence function, and
updating tests accordingly.

Author: lukevalenta

crates/ct_worker/config.schema.json

@@ -64,11 +64,16 @@
                             "type": "string",
                             "description": "Provide a hint to place the log in a specific geographic location. See https://developers.cloudflare.com/durable-objects/reference/data-location/ for supported locations. If unspecified, the Durable Object will be created in proximity to the first request."
                         },
-                        "sequence_interval": {
+                        "sequence_interval_seconds": {
                             "type": "integer",
                             "minimum": 1,
                             "default": 1,
                             "description": "The duration in between sequencing operations, in seconds."
+                        },
+                        "max_pending_entry_holds": {
+                            "type": "integer",
+                            "default": 1,
+                            "description": "The maximum number of times a pending entry can be held back from sequencing to avoid creating partial tiles. If non-zero, pending entries may be delayed by a multiple of sequence interval."
                         }
                     },
                     "required": [

crates/ct_worker/config/src/lib.rs

@@ -28,9 +28,15 @@ pub struct LogParams {
     pub temporal_interval: TemporalInterval,
     pub location_hint: Option<String>,
     #[serde(default = "default_sequence_interval_seconds")]
-    pub sequence_interval: u64,
+    pub sequence_interval_seconds: u64,
+    #[serde(default = "default_max_pending_entry_holds")]
+    pub max_pending_entry_holds: usize,
 }
 
 fn default_sequence_interval_seconds() -> u64 {
     1
 }
+
+fn default_max_pending_entry_holds() -> usize {
+    1
+}