add PyLong* API (3.14+)

[chirizxc]

/close #6015

main (3.13):

into_u128_zero          time:   [33.711 ns 33.971 ns 34.252 ns]
into_u128_small         time:   [34.602 ns 34.859 ns 35.157 ns]
into_u128_u32_max       time:   [34.700 ns 35.231 ns 35.684 ns]
into_u128_u64_max       time:   [40.138 ns 40.795 ns 41.375 ns]
into_u128_max           time:   [39.668 ns 40.320 ns 40.891 ns]
into_i128_zero          time:   [33.628 ns 33.947 ns 34.335 ns]
into_i128_small_pos     time:   [34.595 ns 34.900 ns 35.250 ns]
into_i128_small_neg     time:   [35.660 ns 36.223 ns 36.743 ns]
into_i128_pos_max       time:   [39.891 ns 40.513 ns 41.041 ns]
into_i128_neg_min       time:   [43.970 ns 44.582 ns 45.093 ns]
extract_u128_zero       time:   [20.255 ns 20.341 ns 20.439 ns]
extract_u128_small      time:   [20.208 ns 20.330 ns 20.466 ns]
extract_u128_u32_max    time:   [26.269 ns 26.458 ns 26.674 ns]
extract_u128_u64_max    time:   [30.125 ns 30.322 ns 30.549 ns]
extract_u128_max        time:   [35.379 ns 35.644 ns 35.933 ns]
extract_i128_zero       time:   [20.521 ns 20.602 ns 20.702 ns]
extract_i128_small_pos  time:   [20.630 ns 20.736 ns 20.858 ns]
extract_i128_small_neg  time:   [20.357 ns 20.442 ns 20.539 ns]
extract_i128_pos_max    time:   [34.338 ns 34.568 ns 34.837 ns]
extract_i128_neg_min    time:   [49.427 ns 49.754 ns 50.169 ns]

this PR (3.14):

into_u128_zero          time:   [17.348 ns 17.475 ns 17.617 ns]
into_u128_small         time:   [18.758 ns 18.950 ns 19.163 ns]
into_u128_u32_max       time:   [27.941 ns 28.377 ns 28.762 ns]
into_u128_u64_max       time:   [33.655 ns 34.173 ns 34.633 ns]
into_u128_max           time:   [34.166 ns 34.739 ns 35.296 ns]
into_i128_zero          time:   [17.017 ns 17.154 ns 17.301 ns]
into_i128_small_pos     time:   [19.636 ns 19.818 ns 20.019 ns]
into_i128_small_neg     time:   [29.753 ns 30.247 ns 30.675 ns]
into_i128_pos_max       time:   [34.856 ns 35.374 ns 35.835 ns]
into_i128_neg_min       time:   [34.675 ns 35.254 ns 35.785 ns]
extract_u128_zero       time:   [18.302 ns 18.434 ns 18.571 ns]
extract_u128_small      time:   [18.654 ns 18.771 ns 18.904 ns]
extract_u128_u32_max    time:   [19.758 ns 19.915 ns 20.084 ns]
extract_u128_u64_max    time:   [23.769 ns 23.975 ns 24.193 ns]
extract_u128_max        time:   [23.988 ns 24.128 ns 24.284 ns]
extract_i128_zero       time:   [19.126 ns 19.261 ns 19.405 ns]
extract_i128_small_pos  time:   [19.004 ns 19.157 ns 19.316 ns]
extract_i128_small_neg  time:   [18.819 ns 18.933 ns 19.058 ns]
extract_i128_pos_max    time:   [24.424 ns 24.593 ns 24.776 ns]
extract_i128_neg_min    time:   [24.007 ns 24.147 ns 24.299 ns]

cmd:

cargo bench --bench bench_int128 -- --warm-up-time 3 --measurement-time 5 2>& | grep -E '^(into|extract)_[a-z0-9_]+\s+time:'

benchmark	3.13 (ns)	3.14 (ns)	speedup
into_u128_zero	33.97	17.48	1.94×
into_u128_small	34.86	18.95	1.84×
into_u128_u32_max	35.23	28.38	1.24×
into_u128_u64_max	40.80	34.17	1.19×
into_u128_max	40.32	34.74	1.16×
into_i128_zero	33.95	17.15	1.98×
into_i128_small_pos	34.90	19.82	1.76×
into_i128_small_neg	36.22	30.25	1.20×
into_i128_pos_max	40.51	35.37	1.15×
into_i128_neg_min	44.58	35.25	1.26×
extract_u128_zero	20.34	18.43	1.10×
extract_u128_small	20.33	18.77	1.08×
extract_u128_u32_max	26.46	19.91	1.33×
extract_u128_u64_max	30.32	23.98	1.26×
extract_u128_max	35.64	24.13	1.48×
extract_i128_zero	20.60	19.26	1.07×
extract_i128_small_pos	20.74	19.16	1.08×
extract_i128_small_neg	20.44	18.93	1.08×
extract_i128_pos_max	34.57	24.59	1.41×
extract_i128_neg_min	49.75	24.15	2.06×

[ngoldbaum]

Did a quick pass and spotted a couple issues.