feat: experiment log stream, to file and UI

Adds a few new logging utility classes. One to save to files with a date, one to support optional fields in formats, last to filter partial log messages.

ref: N25B-401

.logging_config.yaml

@@ -1,36 +1,56 @@
 version: 1
 
 custom_levels:
-  OBSERVATION: 25
-  ACTION: 26
+  OBSERVATION: 24
+  ACTION: 25
+  CHAT: 26
   LLM: 9
 
 formatters:
   # Console output
   colored:
-    (): "colorlog.ColoredFormatter"
+    class: colorlog.ColoredFormatter
     format: "{log_color}{asctime}.{msecs:03.0f} | {levelname:11} | {name:70} | {message}"
     style: "{"
     datefmt: "%H:%M:%S"
 
   # User-facing UI (structured JSON)
-  json_experiment:
-    (): "pythonjsonlogger.jsonlogger.JsonFormatter"
+  json:
+    class: pythonjsonlogger.jsonlogger.JsonFormatter
     format: "{name} {levelname} {levelno} {message} {created} {relativeCreated}"
     style: "{"
 
+  # Experiment stream for console and file output, with optional `role` field
+  experiment:
+    class: control_backend.logging.OptionalFieldFormatter
+    format: "%(asctime)s %(levelname)s %(role?)s %(message)s"
+    defaults:
+      role: "-"
+
+filters:
+  # Filter out any log records that have the extra field "partial" set to True, indicating that they
+  #  will be replaced later.
+  partial:
+    (): control_backend.logging.PartialFilter
+
 handlers:
   console:
     class: logging.StreamHandler
     level: DEBUG
     formatter: colored
+    filters: [partial]
     stream: ext://sys.stdout
   ui:
     class: zmq.log.handlers.PUBHandler
     level: LLM
-    formatter: json_experiment
+    formatter: json
+  file:
+    class: control_backend.logging.DatedFileHandler
+    formatter: experiment
+    filters: [partial]
+    file_prefix: experiment_logs/experiment
 
-# Level of external libraries
+# Level for external libraries
 root:
   level: WARN
   handlers: [console]
@@ -39,3 +59,6 @@ loggers:
   control_backend:
     level: LLM
     handlers: [ui]
+  experiment:
+    level: DEBUG
+    handlers: [ui, file]