Optimize JSON encoding of numbers

[jcrist]

This further optimizes the JSON encoding of integers and floats.

[jcrist]

A quick benchmark:

import random
from time import perf_counter_ns

from orjson import dumps
from msgspec.json import encode

N = 10000
M = 2000
random.seed(42)
for header, scale, func in [
    ("Small Integers:", 1000, random.randint),
    ("Large Integers:", int(1e16), random.randint),
    ("Small Floats:", 1000, random.uniform),
    ("Large Floats:", int(1e16), random.uniform),
]:
    print(header)
    data = [func(-scale, scale) for _ in range(N)]

    start = perf_counter_ns()
    for _ in range(M):
        encode(data)
    stop = perf_counter_ns()
    print(f"- msgspec: {(stop - start) / (1000 * M):.2f} us")

    start = perf_counter_ns()
    for _ in range(M):
        dumps(data)
    stop = perf_counter_ns()
    print(f"- orjson: {(stop - start) / (1000 * M):.2f} us")

Before

$ python bench.py
Small Integers:
- msgspec: 122.89 us
- orjson: 137.58 us
Large Integers:
- msgspec: 228.17 us
- orjson: 376.78 us
Small Floats:
- msgspec: 374.01 us
- orjson: 355.98 us
Large Floats:
- msgspec: 404.31 us
- orjson: 395.41 us

This PR

$ python bench.py
Small Integers:
- msgspec: 132.78 us
- orjson: 143.62 us
Large Integers:
- msgspec: 189.28 us
- orjson: 377.78 us
Small Floats:
- msgspec: 351.13 us
- orjson: 356.19 us
Large Floats:
- msgspec: 391.72 us
- orjson: 395.72 us