fix: [2.4] use the object heap to keep the min ddl ts order

[SimFG]

• issue: [Bug]: Concurrent ddl may break the timetick rule at rootcoord. #39002
• pr: fix: use the object heap to keep the min ddl ts order #39118

[mergify]

@SimFG E2e jenkins job failed, comment /run-cpu-e2e can trigger the job again.

[codecov]

Codecov Report

Attention: Patch coverage is 90.26549% with 11 lines in your changes missing coverage. Please review.

Project coverage is 80.43%. Comparing base (af22644) to head (c140d4e).
Report is 4 commits behind head on 2.4.

Files with missing lines	Patch %	Lines
pkg/util/typeutil/heap.go	88.76%	8 Missing and 2 partials ⚠️
internal/rootcoord/scheduler.go	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.4   #39193      +/-   ##
==========================================
- Coverage   80.44%   80.43%   -0.01%     
==========================================
  Files        1077     1078       +1     
  Lines      169731   169838     +107     
==========================================
+ Hits       136534   136615      +81     
- Misses      28713    28724      +11     
- Partials     4484     4499      +15     

Files with missing lines	Coverage Δ
internal/rootcoord/task.go	96.15% <100.00%> (+0.20%)	⬆️
internal/rootcoord/scheduler.go	94.69% <94.11%> (-0.22%)	⬇️
pkg/util/typeutil/heap.go	88.76% <88.76%> (ø)

... and 34 files with indirect coverage changes

[SimFG]

/run-cpu-e2e

[xiaofan-luan]

/lgtm
/approve

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: SimFG, xiaofan-luan

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• internal/rootcoord/OWNERS [xiaofan-luan]
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