Improved API of mmap

[ritchie46]

Two changes.

1. expose more information on the FileMetaData.

I wanted to know how many Chunks there are in the IPC file. This also exposes the size attribute as that can also be valuable information.

If they are an invariant for unsafe code, I can expose them via functions?

2. use Arc

There was an assumption that Arc<Mmap implements Clone + AsRef<[u8]. It does not. Calling as_ref on an Arc<T> gives us T, which was opaque to us.

Changed the function signature so that we can pass an Arc<Mmap>.

[codecov]

Codecov Report

Merging #1205 (fed029b) into main (5711cfc) will increase coverage by 0.01%.
The diff coverage is 93.61%.

@@            Coverage Diff             @@
##             main    #1205      +/-   ##
==========================================
+ Coverage   83.53%   83.54%   +0.01%     
==========================================
  Files         368      368              
  Lines       37448    37448              
==========================================
+ Hits        31283    31287       +4     
+ Misses       6165     6161       -4     

Impacted Files	Coverage Δ
src/io/ipc/read/reader.rs	96.32% <ø> (ø)
src/mmap/mod.rs	84.84% <76.92%> (ø)
src/ffi/mmap.rs	96.74% <100.00%> (ø)
src/bitmap/utils/slice_iterator.rs	97.56% <0.00%> (-1.22%)	⬇️
src/io/ipc/read/file_async.rs	61.19% <0.00%> (+0.74%)	⬆️
src/io/ipc/read/stream_async.rs	76.71% <0.00%> (+2.05%)	⬆️

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[ritchie46]

I will update the tests tonight.