Pub/sub abstraction: decouple from Pulsar (#751)

Remove Pulsar-specific concepts from application code so that
the pub/sub backend is swappable via configuration.

Rename translators:
- to_pulsar/from_pulsar → decode/encode across all translator
  classes, dispatch handlers, and tests (55+ files)
- from_response_with_completion → encode_with_completion
- Remove pulsar.schema.Record from translator base class

Queue naming (CLASS:TOPICSPACE:TOPIC):
- Replace topic() helper with queue() using new format:
  flow:tg:name, request:tg:name, response:tg:name, state:tg:name
- Queue class implies persistence/TTL (no QoS in names)
- Update Pulsar backend map_topic() to parse new format
- Librarian queues use flow class (persistent, for chunking)
- Config push uses state class (persistent, last-value)
- Remove 15 dead topic imports from schema files
- Update init_trustgraph.py namespace: config → state

Confine Pulsar to pulsar_backend.py:
- Delete legacy PulsarClient class from pubsub.py
- Move add_args to add_pubsub_args() with standalone flag
  for CLI tools (defaults to localhost)
- PulsarBackendConsumer.receive() catches _pulsar.Timeout,
  raises standard TimeoutError
- Remove Pulsar imports from: async_processor, flow_processor,
  log_level, all 11 client files, 4 storage writers, gateway
  service, gateway config receiver
- Remove log_level/LoggerLevel from client API
- Rewrite tg-monitor-prompts to use backend abstraction
- Update tg-dump-queues to use add_pubsub_args

Also: pubsub-abstraction.md tech spec covering problem statement,
design goals, as-is requirements, candidate broker assessment,
approach, and implementation order.

trustgraph-base/trustgraph/log_level.py

@@ -1,6 +1,6 @@
 
 from enum import Enum
-import _pulsar
+
 
 class LogLevel(Enum):
     DEBUG = 'debug'
@@ -10,11 +10,3 @@ class LogLevel(Enum):
 
     def __str__(self):
         return self.value
-
-    def to_pulsar(self):
-        if self == LogLevel.DEBUG: return _pulsar.LoggerLevel.Debug
-        if self == LogLevel.INFO: return _pulsar.LoggerLevel.Info
-        if self == LogLevel.WARN: return _pulsar.LoggerLevel.Warn
-        if self == LogLevel.ERROR: return _pulsar.LoggerLevel.Error
-        raise RuntimeError("Log level mismatch")
-