[AMORO-2977]Mixed-Format Unkeyed Table will read the full amount of data even if configured with 'scan.startup.mode'='latest'

[lklhdu]

Why are the changes needed?

Fix #2977.

Brief change log

• When 'scan.startup.mode'='latest' is configured, read the unkeyed amoro table of type mixed-format based on the current snapshot ID

How was this patch tested?

• Add some test cases that check the changes thoroughly including negative and positive cases if possible

• Add screenshots for manual tests if appropriate

• Run test locally before making a pull request

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32.83%. Comparing base (bdd798c) to head (24e44b3).
Report is 7 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2978      +/-   ##
============================================
- Coverage     32.85%   32.83%   -0.02%     
- Complexity     3822     3824       +2     
============================================
  Files           557      557              
  Lines         46184    46226      +42     
  Branches       6099     6107       +8     
============================================
+ Hits          15173    15180       +7     
- Misses        29818    29852      +34     
- Partials       1193     1194       +1     

Flag	Coverage Δ
core	32.83% <ø> (-0.02%)	⬇️

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[zhoujinsong]

LGTM.

Thanks for the contribution!