Optimize imports

[MichaelOwenDyer]

Summary

This PR fixes some instances of redundant or deprecated path prefixes in the codebase.
This is a new PR after I screwed up the git history of #1422, sorry about that.

Motivation

Code style.

Details

• Some numeric constants are currently imported from core, such as core::u64::MAX or core::f64::EPSILON. Clippy suggests that these be changed to the newer associated constants on the types themselves, e.g. u64::MAX and f64::EPSILON. Also, method calls like u64::max_value() have likewise been replaced with u64::MAX.
• Some types are currently fully qualified despite a matching import. These redundant prefixes have been removed.
• Some paths are currently prefixed with :: unnecessarily, which has been removed.
• Instances of -f64::INFINITY have been replaced with f64::NEG_INFINITY.

[dhardy]

Thanks