fix(expr): incorrect decimal rounding due to rust_decimal bug

[jon-chuang]

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What's changed and what's your intention?

Rust decimal bug allows rounding past 28 significant digits which is its maximum.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features).
• I have demonstrated that backward compatibility is not broken by breaking changes and created issues to track deprecated features to be removed in the future. (Please refer the issue)
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

#7815 (comment)

[jon-chuang]

fixed here: paupino/rust-decimal#575, but our hotfix is just as good.

[codecov]

Codecov Report

Merging #7819 (ee8a7e8) into main (d6f9e2e) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #7819      +/-   ##
==========================================
- Coverage   71.73%   71.72%   -0.01%     
==========================================
  Files        1106     1106              
  Lines      176247   176249       +2     
==========================================
- Hits       126429   126414      -15     
- Misses      49818    49835      +17     

Flag	Coverage Δ
rust	71.72% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/expr/src/vector_op/round.rs	100.00% <100.00%> (ø)
src/batch/src/executor/group_top_n.rs	68.23% <0.00%> (-6.48%)	⬇️
src/meta/src/hummock/mock_hummock_meta_client.rs	63.95% <0.00%> (-0.51%)	⬇️
src/common/src/field_generator/mod.rs	74.50% <0.00%> (-0.50%)	⬇️
src/object_store/src/object/mem.rs	86.87% <0.00%> (-0.39%)	⬇️
src/object_store/src/object/mod.rs	51.30% <0.00%> (-0.22%)	⬇️
src/storage/src/hummock/compactor/mod.rs	80.85% <0.00%> (-0.20%)	⬇️
src/storage/src/hummock/sstable_store.rs	64.73% <0.00%> (-0.16%)	⬇️
src/common/src/cache.rs	97.15% <0.00%> (-0.11%)	⬇️
src/meta/src/hummock/manager/mod.rs	78.14% <0.00%> (-0.06%)	⬇️
... and 2 more

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