Minor: Consolidate int96 stats roundtrip test (#8034)

# Which issue does this PR close?

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enhancements and this helps us generate change logs for our releases.
You can link an issue to this PR using the GitHub syntax.

- Closes #NNN.

# Rationale for this change

I was slightly annoyed that the int96 stats roundtrip test was not part
of the other arrow-reader tests

You have to run it separately:
```shell
cargo test --test int96_stats_roundtrip
```

Let's just move it to the arrow-reader tests, so it is run with the
other tests so
1. It is easier to find
2. It takes slightly less time to build and test the parquet crate



```shell
cargo test --test arrow_reader
```


# What changes are included in this PR?
1. Move the tests

# Are these changes tested?

Yes, by CI

# Are there any user-facing changes?
No

Author: alamb

parquet/tests/int96_stats_roundtrip.rs renamed to parquet/tests/arrow_reader/int96_stats_roundtrip.rs

@@ -41,6 +41,7 @@ use tempfile::NamedTempFile;
 mod bad_data;
 #[cfg(feature = "crc")]
 mod checksum;
+mod int96_stats_roundtrip;
 mod statistics;
 
 // returns a struct array with columns "int32_col", "float32_col" and "float64_col" with the specified values