Rework the Mono and IL2CPP support around per-build offset profiles

[ero-qt]

The Unity support currently guesses layouts: versions from FileVersion thresholds and memory string scans, offsets from four hand-kept eras per backend. A wrong guess is indistinguishable from "not loaded yet" and shows up as an infinite wait.

Some concrete problems:

• Unity 2023.x IL2CPP matches no arm of the version detection and falls back to Version::Base, the oldest layout.
• Mono version detection on ELF/Mach-O silently defaults to V2 when its string scan misses.
• IL2CPP attaches on Windows x64 only; nothing below UnityPointer caches; no nested classes or generic instances.

The plan:

• Identify instead of guessing: Mono by the runtime binary's identity (PE debug GUID, ELF build-id, Mach-O UUID), IL2CPP by (Unity version, pointer size), since GameAssembly.dll is compiled per game and has no identity of its own.
• Offsets become data: per-build profiles generated offline from Unity's own symbols, compiled into static tables. Supporting a new build is a data drop, not new code.
• One shared metadata walk over both runtimes, with a small set of per-runtime operations for where they genuinely diverge.
• An unmeasured player takes the nearest measured build at or below its Unity version, which replaces the version tables: IL2CPP in Attach IL2CPP games through the nearest measured build #160, Mono in Attach Mono games through the nearest measured build #166. An unknown Mono binary is still reported with what was read. The tables only hold the builds where a layout changes: Mono in Attach Mono games through the nearest measured build #166, IL2CPP in Keep only the IL2CPP builds where the layout changes #167.

Module::attach(process, version) goes with the tables on both sides, replaced by attach(process, profile) with public measured profiles. Follow-ups are tracked separately: managed string and collection reads in #149, Linux and Mac Mono builds in #154, the scene manager and time manager rework and engine-shared extraction later.

PRs

In order, each building on the ones before it; every body says what it depends on. #160 stands alone on master.

• Add build identity reads for PE, ELF and Mach-O #142
• Add measured offsets for known mono builds #143
• Add measured offsets for known IL2CPP builds #144
• Attach IL2CPP games through the nearest measured build #160
• Add IL2CPP builds at the layout boundaries #163
• Share one metadata walk between Mono and IL2CPP #145
• Resolve nested classes, generic field counts, and inherited statics #146
• Attach Mono games through the nearest measured build #166
• Keep only the IL2CPP builds where the layout changes #167