fix(streaming): wrap from_json in try/except in non-beta message streaming

[rmotgi1227]

Summary

The beta streaming path (_beta_messages.py) already wraps from_json in a try/except ValueError that surfaces a clear, actionable error when the model emits malformed partial JSON during tool use. The non-beta path (_messages.py) made the same from_json call with no error handling, so malformed JSON propagated as a raw jiter internal error (ValueError: expected ident at line 1 column 11) with no context about what went wrong or what to do.

Change

src/anthropic/lib/streaming/_messages.py — wrap the from_json(json_buf, partial_mode=True) call in try/except ValueError and re-raise with the raw JSON buffer and a retry suggestion, mirroring _beta_messages.py lines 500–510 exactly.

Before:

if json_buf:
    content.input = from_json(json_buf, partial_mode=True)

After:

if json_buf:
    try:
        content.input = from_json(json_buf, partial_mode=True)
    except ValueError as e:
        raise ValueError(
            f"Unable to parse tool parameter JSON from model. Please retry your request or adjust your prompt. Error: {e}. JSON: {json_buf.decode('utf-8')}"
        ) from e

The error message wording is copied verbatim from the beta path so error handling is consistent across both streaming code paths.