Migrate to KHook + misc dev

[Vauff]

• Added custom hud API for plugin use
• Switched from signature to schema manipulator to construct CTakeDamageInfo
• Added a fix for competitive cooldowns always being applied by the game
• Made player_connect obey cs2f_map_steamids_enable
• Migrated to KHook (Migrate to KHook #464)
  • This significantly simplifies full compatibility with other Metamod plugins
  • There may technically still be some edge cases like shared patches/mid-hooks, but realistically these would be very rare & specific instances can be handled in other ways
  • For more details, see Provide an alternative to SourceHook alliedmodders/metamod-source#223
• Updated signatures for 2026-09-09 CS2 update
• Overhauled map migrations to fix an out-of-bounds rendermode issue & run cleanly during map load when possible, this is similar to Stripper and now possible thanks to KHook
• Overhauled the custom cfg parser to skip the command buffer, and process changes immediately
• Added an additional early cfg execution, to ensure map migrations have access to correct cvar values for the upcoming map
• Allowed rendermode migrations to run independent of map update time
  • Index-based rendermodes only come from the S1 map importer, S2 Hammer always uses enum-named render modes, so we can confidently assume that new maps will not be caught off by this, while we can also extend this migration to new/recently updated ports
• Hardened map download queue logic & added delay to avoid Steam rate limit
  • Hitting the rate limit was problematic because it could break required on-demand downloads elsewhere

AI disclosure: Substantially used for RE in the competitive cooldown kick fix, its findings have proven themselves on a live server