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**

No source files or tests are named. Start by reproducing the failure with the monthly nyctaxi Parquet files and inspect the Arrow-rs schema-merging entry point; done means schemas containing Int64 and Float64 passenger_count merge successfully using Float64.

Written by the indexing model from the issue text.