gh-126868: Add freelist for compact ints to _PyLong_New

[eendebakpt]

We add freelist support to _PyLong_New (this was missed/left out in #126868). On the pyperformance suite this increases the percentage of allocations from freelist by roughly 1%. For comparison, the addition of the freelist to _PyLong_FromMedium increased the percentage by roughly 20%. Also note that _PyLong_New is used in the new PyLongWriter_Create (see https://peps.python.org/pep-0757/), so usage with external packages might be a bit higher.

Microbenchmark:

import pyperf

def bench_lshift(loops):
    range_it = range(loops)
    t0 = pyperf.perf_counter()
    for ii in range_it:
        _ = ii << 2
    return pyperf.perf_counter() - t0

if __name__ == "__main__":
    runner = pyperf.Runner()
    runner.bench_time_func("bench_lshift", bench_lshift)

results in:

Mean +- std dev: [main] 44.7 ns +- 3.0 ns -> [pr] 40.9 ns +- 2.3 ns: 1.09x faster

• Issue: Add freelist for compact int objects #126868