Rework `ParquetExec::metadata_size_hint`

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
Currently `metadata_size_hint` passed to `ParquetExec` has the following issues:

- **single value:** It is a single value, but a single `ParquetExec` may contain multiple files. These files may require different hints.
- **serialization:** The value is dropped during protobuf serialization.

Now these two issues are unrelated, but it feels like fixing both in one go makes sense.

**Describe the solution you'd like**
Move `metadata_size_hint` to `FileScanConfig::file_groups` > `PartitionedFile`:

https://github.com/apache/arrow-datafusion/blob/d11820aa256284f9a817c7b699a548f9c3e1c399/datafusion/core/src/datasource/listing/mod.rs#L51-L64

**Describe alternatives you've considered**
Leaving the status quo.

**Additional context**
\-

Start with ParquetExec::metadata_size_hint and the PartitionedFile definition in datafusion/core/src/datasource/listing/mod.rs. Trace how file_groups and ParquetExec are serialized through protobuf, then verify that each file can retain its own metadata size hint and that the hint survives serialization and deserialization.

Written by the indexing model from the issue text.