Smooth UnspentCostBucket budget spending

[komarevtsev-d]

#5095
Register() no longer consumes budget in a single fixed way for the gap between the minimum and maximum budget spend. It now picks a desired spend by interpolating between minBudgetSpend and maxBudgetSpend using Smootherstep(CurrentBudget / MaxBudget). Consumption should be higher when the budget is fuller.

For interpolation i chose the smootherstep. It is slightly faster than sigmoid and simpler to use, as it is conveniently positioned relative to the y-axis (unlike sigmoid).

Added a benchmark that compares sigmoid to smoothstep functions. Results are:

----------- Sigmoid_Benchmark ---------------
 samples:       39338
 iterations:    955260195
 iterations hr:    955M
 run time:      5.003712421
 per iteration: 12.32858252 cycles
----------- Smoothstep_Benchmark ---------------
 samples:       99311
 iterations:    6088175031
 iterations hr:    6.09G
 run time:      5.009607195
 per iteration: 1.947897513 cycles
----------- Smootherstep1_Benchmark ---------------
 samples:       96192
 iterations:    5711827521
 iterations hr:    5.71G
 run time:      5.008432135
 per iteration: 2.079131814 cycles
----------- Smootherstep2_Benchmark ---------------
 samples:       93695
 iterations:    5419081671
 iterations hr:    5.42G
 run time:      5.00840317
 per iteration: 2.190996133 cycles
----------- Smootherstep3_Benchmark ---------------
 samples:       79463
 iterations:    3897871071
 iterations hr:    3.9G
 run time:      5.007022594
 per iteration: 3.047205232 cycles

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🟢 linux-x86_64-relwithdebinfo target: cloud/disk_manager/ (test time: 225s): all tests PASSED for commit b80efe3.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
1091	1091	0	0	0	0	0

🟢 linux-x86_64-relwithdebinfo target: cloud/tasks/,cloud/storage/ (test time: 432s): all tests PASSED for commit b80efe3.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
865	865	0	0	0	0	0

🔴 linux-x86_64-relwithdebinfo target: cloud/blockstore/ (test time: 1545s): some tests FAILED for commit b80efe3.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
5961	5959	0	1	0	1	0

🟢 linux-x86_64-relwithdebinfo target: cloud/blockstore/ (test time: 44s): all tests PASSED for commit b80efe3.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
39	39	0	0	0	0	0

🟢 linux-x86_64-relwithdebinfo target: cloud/filestore/ (test time: 4793s): all tests PASSED for commit b80efe3.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
3510	3510	0	0	0	0	0