[53.0.0_maintenance] fix: decimal conversion looses value on lower precision (#6836)

[andygrove]

Which issue does this PR close?

Part of #6887

Rationale for this change

Backports #6836 to 53.x.x

What changes are included in this PR?

Are there any user-facing changes?

[alamb]

Thanks @andygrove -- I am looking at the CI failures now

[alamb]

The clippy issue seems to have been fixed by #6791 -- I will create a backport PR for that:

• PR: [53.0.0_maintenance] fix clippy on 53.0.0_maintenance branch #6940

[alamb]

Here is a proposed workaround for the docs failure:

• [53.0.0_maintenance] Workaround py03 doc failure #6941

[alamb]

The archery test faolure appears to be some transient failure: https://github.com/apache/arrow-rs/actions/runs/12603098780/job/35127463445?pr=6936

Integration: Test: Result
  ################# FAILURES #################
  FAILED TEST: dictionary Rust producing,  Rust consuming
  <class 'RuntimeError'>: Command failed: /build/rust/debug/flight-test-integration-client --host localhost --port=36655 --path /tmp/arrow-integration-o2tv9_3_/generated_dictionary.json
  With output:
  --------------
  Error: tonic::transport::Error(Transport, ConnectError(ConnectError("tcp connect error", Os { code: 111, kind: ConnectionRefused, message: "Connection refused" })))
  
  --------------  

I will retrigger to be sure

[alamb]

Looks good to me -- thanks @andygrove