Improve schema merging

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

I am trying to work with the nyctaxi parquet data set which has one file per month. Over time, some of the types have changed. For example `passenger_count` started out as `Int64` and was later changed to `Float64`.

Arrow-rs can not merge these schemas.

Other solutions (such as DuckDB) will merge these schemas and pick the least restrictive type (`Float64`).

**Describe the solution you'd like**

**Describe alternatives you've considered**

**Additional context**

Non vengono indicati file sorgente o test. Inizia riproducendo il problema con i file Parquet mensili di nyctaxi e ispeziona l’entry point per l’unione degli schemi di Arrow-rs; il lavoro è completato quando gli schemi contenenti Int64 e Float64 per passenger_count vengono uniti correttamente usando Float64.

Scritto dal modello di indicizzazione a partire dal testo della issue.