IPv4Address: constexpr support

Problem:
- IPv4Address class cannot be used in a compile-time context.
- A union is used by initializing one of the members and reading the
  non-active member. This is undefined behavior and not permitted in a
  `constexpr` context.

Solution:
- Eliminate undefined behavior by changing to a simple `u32` for
  storage instead of the union and performing mask/shift calculations
  for obtaining the individual octets.
- Decorate functions with `constexpr` where possible. Currently string
  formatting and optionals are not `constexpr`-capable so functions
  using those are left out.
- Modify tests to validate functionality in a `constexpr` context in
  addition to the run-time tests already being run. This ensures that
  functionality is the same in both contexts.

0 files changed, 0 insertions, 0 deletions