Silence duplicate JSON parse error logs

[hemanth-asirvatham]

Motivation

• Remove repeated JSON parse warnings that were being emitted multiple times and double-printed.
• Align JSON parse error logging behaviour with other error types (timeouts, rate limits, connections) so only the first occurrence is prominently logged and later occurrences are silenced and tracked.

Description

• Added a first_json_parse_logged flag in src/gabriel/utils/openai_utils.py to track whether a JSON parse warning has been emitted.
• Introduced a _log_json_parse_once helper which emits a first-occurrence message (via _emit_first_error) and then silences subsequent JSON parse errors by logging them at debug level.
• Replaced the direct _emit_first_error call in the JSONParseError handler with _log_json_parse_once(error_detail).
• Removed a duplicate logger.warning for non-timeout API errors to avoid double emission of the same warning.

Testing

• No automated tests were run for this change.

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Codex Task

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