process wrong response format

[iptton]

• Introduce 'lastParseFailedResponse' to store the failed response.
• Log a detailed error message when a null response is encountered.
• Add a check at the end of the stream to notify the user if no successful parse occurred.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 12.18%. Comparing base (d1e6a93) to head (55c7891). Report is 1 commits behind head on master.

Files	Patch %	Lines
...c/unitmesh/devti/llms/custom/CustomSSEProcessor.kt	0.00%	13 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #122 +/- ## ========================================== - Coverage 12.19% 12.18% -0.01% ========================================== Files 473 473 Lines 11023 11027 +4 Branches 2111 2111 ========================================== Hits 1344 1344 - Misses 9425 9429 +4 Partials 254 254 ```

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