Using fast_float library for faster parsing of 64 decimal strings.

[filipecosta90]

Fixes #8825

We're using the fast_float library1 in our (compiled-in) floating-point fast_float_strtod implementation for faster and more portable parsing of 64 decimal strings.

The single file fast_float.h is an amalgamation of the entire library, which can be (re)generated with the amalgamate.py script (from the fast_float repository) via the command:

python3 ./script/amalgamate.py --license=MIT > $REDIS_SRC/deps/fast_float/fast_float.h

The used commit from fast_float library was the one from https://github.com/fastfloat/fast_float/releases/tag/v3.10.1

Still TODO:

• finish the simplest possible makefile of fast_float ( but production ready )
• validate the performance impact of this change via the benchmark SPEC
• validate with @lemire that this is the best approach for including the fast_float lib
• Fix the error raised in Added missing FASTFLOAT_ALLOWS_LEADING_PLUS ifdef check in parse_infnan fastfloat/fast_float#183 on fast_float original code and update fast_float.h
• check gcc 12 baseline performance

[lemire]

Upgrading to 3.10.1 might be better: https://github.com/fastfloat/fast_float/releases/tag/v3.10.1

[lemire]

If you want to catch potential errors, you ought to add..

 if(answer.ec != std::errc()) { /* do something */ }

(Note that the library follows the C++ standard so that's how we handle errors. We did not design this approach.)

[lemire]

This looks simple enough. My main concern is that you do not check for the error field after parsing. If you only rarely invoke strtod, then switching to the canonical fast_float API might be simpler. Whether this matters for your application, I do not know.

Note that fast_float relies on the C++17 standard API, so adopting the fast_float API is not akin to vendor lockin... it is a standard!!!

[lemire]

Note that the fast_float library has been adopted by webkit (Apple Safari) and other important systems such as GCC.

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