DAOS-16574 vos: shrink DTX table blob size

[Nasf-Fan]

Use 4KB blob for committed DTX table and 16KB for active DTX table. It is more efficient for lower allocator and reduce the possibility of space allocation failure when space pressure.

Simplify vos_dtx_commit logic and code cleanup.

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[github-actions]

Ticket title is 'After performing a pool extend, noticing rebuild timeouts on soak offline harasser testing [2.6.1-rc1]'
Status is 'In Progress'
Labels: 'manual_test,soak,2.6.1_issue'
https://daosio.atlassian.net/browse/DAOS-16574

[Nasf-Fan]

Ping reviewers, thanks!

[NiuYawei]

I'm wondering if we should introduce 2 slabs for these 2 sizes.

[Nasf-Fan]

That is possible, but not sure how much it will help since the table blob is not allocated for each DTX entry, instead, it will be allocated per tens of or hundreds of DTX entries.