feat(fmt): support fmt::Writers when writing ini to a Writer

[iiian]

Allows for

ini.to_string()
ini.write_to_fmt(&mut std::fmt::Writer)
ini.write_to_policy_fmt(&mut std::fmt::Writer, EscapePolicy)
ini.write_to_opt_fmt(&mut std::fmt::Write, WriteOption)

Context

I'm working with a very laggy remote Windows file system. Each individual R/W request has about 2 seconds delay before actually getting serviced. This means the streaming write!-based implementation of write_to_opt() is resulting in something like an O(n) slow-down where n is the # lines in the file. Introducing a fmt::Writer version, write_to_opt_fmt, lets me buffer the entire ini as a String and then fire it in one shot, resulting in a 75x performance improvement in my test scenario with an INI 462 lines long.

[iiian]

cargofmt strikes

[iiian]

this impl is a verbatim scrape of the impl Ini block that defines the likes of write_to, write_to_policy, write_to_opt, but replaces each with std::fmt::Writer instead of std::io::Writer

[iiian]

Honestly this is negotiable, it could be nice to have but I'm perfectly fine cutting it out.

[zonyitoo]

Please resolve the windows CI build failure (\r\n issue).

[zonyitoo]

Still broken.

[iiian]

Hrm... I'm just not sure why this isn't working. I loaded rust-ini up on my Windows 11 machine, with supporting VisualC++ tooling -- all the unit tests are still passing. It seems to boil down to my inability to get the rust runtime to treat

r"
hello
world
"

as having CRLFs, even though there are unit tests above mine that seemingly do the exact same thing.

Any ideas?

[zonyitoo]

You may consider add an option to the write_to_fmt call, which will force line-break to use \n.