chore: improve message summarization with error handling

[muralov]

Description
Improve message summarizer for error cases by implementing fallback scenario.

Changes proposed in this pull request:

• implement fallback mechanism in error cases
• add unit tests

[github-actions]

Note(s) for PR Auther:

• The integration test will be skipped for the PR. You can trigger it manually after adding the label: run-integration-test.
• The evaluation test will be skipped for the PR. You can trigger it manually after adding the label: evaluation requested.
• If any changes are made to the evaluation tests data, make sure that the integration tests are working as expected.
• If any changes are made to how to run the unit tests, make sure to update the steps for unit-tests in the create-release.yml workflow as well.

Note(s) for PR Reviewer(s):

• Make sure that the integration and evaluation tests are working as expected.