fix: parse "KEEP FIRING FOR"

[fengys1996]

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What's changed and what's your intention?

This pull request updates the SQL trigger syntax to use the phrase KEEP FIRING FOR instead of the previous single keyword KEEP_FIRING_FOR.

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.