Add code quality improvements, manually and with clang-tidy/clang-format

[red-robby]

These changes are minimal and include:

• Marking members functions as const/noexcept if appropriate.
• Using the standard types from <cstdint> (and prepending all such types with std::).
• Removing constructors that just initialized member variables. Instead, we initialize them where they are declared.
• Replacing some constants expressed as macros with equivalent (type safe) constexpr values.

No code logic has been modified.