Document mnDiagram distance and number formatting helpers

[itsgrimetime]

Summary

• document the five mnDiagram distance and number-formatting helpers at their declarations in mndiagram.h
• remove inaccurate inline claims about display units, caps, and time formatting
• align the mnDiagram_FormatDecimalNumber prototype parameter name with its definition
• keep symbol documentation inline, following the layout agreed in Doxygen gotchas #2938; this PR adds no .dox redeclarations

Runtime validation

The documented boundary and formatting contracts were checked with 73 controlled Dolphin 2509 / GALE01 v1.02 cases, including both saved-language branches.

Build verification

• rebased onto current upstream/master
• ninja
• python configure.py progress
• 1130/1130 objects matching and linked
• rebuilt DOL SHA-1: 08e0bf20134dfcb260699671004527b2d6bb1a45
• git diff --check
• clang-format clean

[decomp-dev]

Report for GALE01 (f7cf71c - 30063ed)

No changes

[ribbanya]

I'm not sure this is something we want to do, see #2938. We might be forced to place documentation at the definition. I'm not really sure what the best layout is but it's not great to churn one way and then the other. We need to look more at how large/stable codebases are handling this problem.

[ribbanya]

The main reason for using .dox files was to document struct fields separate from the definition, mostly because HAL likes to declare 2000-line structs that are annoying to wade through if each field also has multi-line documentation. I really don't know what the best solution is.

[itsgrimetime]

makes sense. i'll play around with some stuff and do some thinking as well and see if I can't come up with some ideas

[itsgrimetime]

Updated this onto current master. The helper documentation now lives on the real declarations in mndiagram.h, with no external .dox redeclarations, following the symbol-documentation layout agreed in #2938. The rebased branch still reproduces the expected DOL and remains 100% matched/linked.