Żmij 1.2 "the proof is in the printf" released with full to_chars implementation, formal verification, improved performance and more

[Żmij](https://github.com/vitaut/zmij) 1.2 is out. It started as a shortest round-trip `double`\-to-string converter; this release makes it a full formatter.

* Scientific, fixed, general and hex notation with a caller-specified precision, matching `printf`'s `%e`, `%f`, `%g` and `%a`.
* `long double`, covering both x87 80-bit extended and IEEE binary128.
* Full FP `std::to_chars` implementation that works in C++14 and is [several times faster and smaller](https://vitaut.net/posts/2026/complete-to-chars/) than typical standard library implementations.
* The main algorithms are now proved correct in Lean 4.
* `float` conversion is about 23% faster than 1.1, `double` is 1-4% faster.
* Initial `constexpr` support.

Release notes: [https://github.com/vitaut/zmij/releases/tag/v1.2](https://github.com/vitaut/zmij/releases/tag/v1.2)

https://redd.it/1wna0z2
@r_cpp