wip: blockbuilder timespan

[ashwanthgoli]

What this PR does / why we need it:

• creates one job per partition to consume records spanning a duration of targetPeriod
• stores the last committed record timestamp as metadata in the commit record, we use this to plan the next job for a partition

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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