scheduler, processor(ticdc): replace some panic with error (#9123)

[ti-chi-bot]

This is an automated cherry-pick of #9123

What problem does this PR solve?

Issue Number: ref #9125

What is changed and how it works?

1. replace some panic with error
2. record startTs in sorter engine

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

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[ti-chi-bot]

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