Experimental parse-display POC

[nyurik]

It may be possible to eliminate a lot of fmt::Display code by using parse-display crate. In the first iteration, it can replace many display traits for the simple cases of constants and formatted inner values. In the more advanced, it should be possible to format iterators, and if the issue I proposed get implemented, might even cover many of the fmt_sse functions.

Note that I made a few unit tests for the migration purposes - just to see that the result is identical. We may want to remove at least some of them later on as being too trivial.

One aspect that may need discussion:

write!(f, "{value}") is not the same as value.fmt(f) because the first case creates a new Formatter instance, whereas the second case reuses the one passed as an argument to Display::fmt function.

In some cases, it may break if formatter contains padding or number formatting configuration that will or won't be passed to the nested object. parse-display seem to always generate a new Formatter, but Oxigraph uses a lot of .fmt calls - which might actually be a bug.

[Tpt]

Hi! Thank you! I am often a bit not at ease with adding macro driven code. I like to keep things simple and a big match seems to me easier to understand and tweak than complex macros and extra dependencies.