MMap support for IPC files

[fabianmurariu]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
We are using polars-arrow and would prefer to move to arrow-rs as we are looking into using Datafusion as well

Describe the solution you'd like
We are dependent on mmap support for IPC format

Describe alternatives you've considered
keep using polars-arrow

Additional context
It looks like Buffer and Bytes have the right functions and support for Custom dealocation

[tustvold]

The docs could definitely be improved, but the way to do this is to use FileDecoder with a buffer constructed from your mmap file - https://docs.rs/arrow-ipc/latest/arrow_ipc/reader/struct.FileDecoder.html

[fabianmurariu]

I'll have a look these days, if it works out I'll raise a PR