Make features explicit, error fixes,

[nyurik]

• Use thiserror for all errors to allow better error reporting
• Make all HTTP errors into proper objects without string formatting -- formatting is delayed until printing, or if not logged by end user, works much faster
• add justfile to simplify development (optional, but useful)
• cleanup CI to make it far simpler (that GH action is not maintained, and not worth it)
• Made cargo.toml explicitly declare all features - instead of auto-exposing optional dependencies as features
• Lastly, it seems fmmap has not been updated for a long time, and because of that it no longer compiles in some cases because of the dependency problems. I submitted a PR, hopefully will be merged/published soonish.

[nyurik]

P.S. My fmmap PR was merged (impressive speed!), but i'm still a bit concerned - that repo is not often maintained, whereas https://github.com/RazrFalcon/memmap2-rs seems to be the latest "standard" in the memmap crates. Is there a reason for fmmap?

[lseelenbinder]

The simple answer about the mmap library is async support @nyurik. It doesn't look like memmap2 supports async, and I didn't want to litter the library with block_in_place calls.

[lseelenbinder]

Looks good once tests pass. 👍

[nyurik]

I'll wait for a day or two to see if fmmap is released - feels kinda bad to use an unreleased dependency