fix(parsers): merge dict tool_input fragments instead of concatenating

[LazarusX]

Summary

• Fix false "Tool call truncated by Kiro API" errors on Write tool calls with large content
• Root cause: when Kiro API sends tool arguments split across multiple tool_input events as dicts, the parser serialized each dict independently and concatenated the JSON strings — producing invalid JSON like {"file_path":"..."}{"content":"..."}
• The brace-counting diagnostic then misidentified this ~130-150 byte invalid JSON as upstream truncation
• Fix accumulates dict fragments via .update() and serializes once at finalize time

Test plan

• All 73 existing parser unit tests pass
• Verified dict fragment scenario (empty start + multiple dict inputs with brace-containing content)
• Verified single dict with stop (immediate finalization)
• Verified string fragment path unchanged
• Live test: large Write tool call with JSON-like patterns in content succeeds without truncation error

Fixes #153

🤖 Generated with Claude Code

[cla-bot]

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[LazarusX]

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