[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?

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

• [ ] Add screenshots for manual tests if appropriate

• [x] 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 :white_check_mark:

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

Additional details and impacted files

```diff @@ 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](https://app.codecov.io/gh/apache/amoro/pull/2978/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | Coverage Δ | | |---|---|---| | [core](https://app.codecov.io/gh/apache/amoro/pull/2978/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache) | `32.83% <ø> (-0.02%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=apache#carryforward-flags-in-the-pull-request-comment) to find out more.

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