Fix custom vsnprint formatting for width, leading zeros, and %X

[emrainey]

The custom core::vsnprint parser does not handle leading zero flags or width limits (e.g. %02X prints as ?2X on target boot logs for the Ethernet MAC address). Additionally, %X is not supported (only lowercase %x is supported which prepends 0x to all hex outputs).

This task will:

• Enhance print_number and print_signed_number to support width, padding, uppercase hex, and signs.
• Update core::vsnprint formatting parser to parse leading zero flags and widths prior to length modifiers.
• Implement %X specifier (uppercase hex without prepending 0x).
• Adjust width calculations for %x and %b to account for prepended prefixes.
• Create unit tests under catch2-vsnprint.cpp to verify all formatting.

[emrainey]

PR #34 has been opened to resolve this issue by introducing corrected padding, width parsing, and uppercase hex support (%X) in the custom core::vsnprint implementation.