String-like object that supports both property and method access patterns.
Exists to maintain backward compatibility while transitioning from method-based to
property-based text access in message objects. In LangChain <v1.0, message text was
accessed via .text() method calls. In v1.0=<, the preferred pattern is property
access via .text.
Rather than breaking existing code immediately, TextAccessor allows both
patterns:
message.text (returns string directly)message.text() (callable, emits deprecation warning)