Explicitly cast constant uint64_ts that lose precision.

[jbapple]

In clang-16, there are warnings like this upon build:

warning: implicit conversion from 'const uint64_t' (aka 'const
unsigned long') to 'double' changes value from 9223372036854775807
to 9223372036854775808 [-Wimplicit-const-int-float-conversion]

Explicit casting fixes those warnings.

[coveralls]

Pull Request Test Coverage Report for Build 3876955097

• 3 of 3 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 93.871%

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Totals
Change from base Build 3876432800:	0.002%
Covered Lines:	2328
Relevant Lines:	2480

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💛 - Coveralls