[Filesystem] Check number of bytes copied.
feature #11857 [Filesystem] Check number of bytes copied. (skigun)

This PR was merged into the 2.6-dev branch.

Discussion
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[Filesystem] Check number of bytes copied.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10838
| License       | MIT
| Doc PR        | n/a

This only test local files (because of `filesize`), wonder if we should include the remote files using `get_headers` in order to get the Content-length for example. However, it will perform an additional request...

Here's a little benchmark for 500 copy from a remote origin file :
- Standard without check -> Time: 47.34 seconds, Memory: 3.75Mb
- Check with `get_headers` ->Time: 1.32 minutes, Memory: 3.75Mb

Commits
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81eca38 [Filesystem] Check number of bytes copied.