Improve digit counting methods

[mborland]

Currently we use binary search tree to figure out the number of digits in a number. Looks like in the case of std::uint32_t we could covert to log calculation with a >15% speedup. I expect similar speedups for uint64_t and __uint128_t where it is more desparately needed.

Closes: #643

[mborland]

Benchmarks showed improvement for the operation, but when run inside the decimal benchmarks it caused decimal32 to slow down by greater than a factor of 2. Continuing to investigate with uint64_t since that has many more operations in the search tree.

[mborland]

Improvements for uint64_t were inconclusive, but using the same method for computing log on uint128_t yielded an about 8% improvement.

[codecov[bot]]

Codecov Report

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[mborland]

Replaced by different method in: https://github.com/cppalliance/decimal/pull/647