Support serving pre-compressed files for static sites

[antonok-edm]

PR Type

Feature

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

Overview

This PR adds the Files::try_compressed() builder method. If a static files service is constructed with that method, each incoming request will automatically check for a pre-compressed .gz, .br, or .zst file on disk, in order of preference according to the Accept-Encoding header, before falling back to the normal uncompressed file. When a compressed file is selected, the Content-Encoding header is populated with the respective compression type, while the Content-Type and Content-Disposition fields retain the original file's values.

There should be no breaking changes here, although I've had to expose some fields in ways that may not be ideal (I'm looking at the SUPPORTED_ENCODINGS list in particular, and perhaps the new features I've copied straight from actix-web - let me know if you have a better idea of how to structure any of that!). Resolved, see #2615 (comment)

Closes #2415

[antonok-edm]

After some reflection, I've realized there's no reason to tie the supported precompression formats here to the supported runtime compression formats in actix-web, since these ones don't actually depend on any additional dependencies. That means there's no need to reference the SUPPORTED_ENCODINGS from actix-web, and no need to have additional features exposed, and it makes things overall a bit neater.

I've pushed those changes.

[lilnasy]

@robjtede miniserve depends on actix-files and would really benefit from this PR merging. Is there something blocking its review?

[robjtede]

Just time allocation. Reviews from interested parties will help massively.

[JohnTitor]

Thank you for the PR and sorry for the delay!
LGTM with some tweaks.