"reload biomes" will now hot reload changes, like on items.

1. YAML tags changed to lowercase

  - Changed yaml:"darkArea" to yaml:"darkarea"
  - Changed yaml:"litArea" to yaml:"litarea"
  - Changed yaml:"requiredItemId" to yaml:"requireditemid"
  - Changed yaml:"usesItem" to yaml:"usesitem"
  - All YAML tags now follow the lowercase convention as requested

2. Implemented Loadable interface methods

  - Added Id() method that returns the biome ID as a string
  - Added Validate() method with proper validation logic
  - Added Filepath() method that returns the individual file path
  - BiomeInfo now satisfies the Loadable[string] interface

3. Refactored to use fileloader.LoadAllFlatFiles pattern

  - Converted from single biomes.yaml file to individual biome files
(e.g., city.yaml, forest.yaml)
  - Changed loading mechanism to use fileloader.LoadAllFlatFiles[string,
*BiomeInfo]()
  - Created individual biome files in _datafiles/world/default/biomes/
directory

I looked at races/mobs/items and tried to follow the same pattern.

Additional fixes and changes:

  - Updated all references to BiomeInfo fields to use the new exported
fields
  - Fixed method calls from Symbol() to GetSymbol() and Name() to Name
field access
  - Fixed the return type of GetBiome() to return *BiomeInfo instead of
BiomeInfo
Also had to fix an unreachable code issue in mutators.go (This was a
compiler error due to unreachable code after line 49 because of a
'return false') This may be intentional, but the compiler will not make
the binary without this change.

Added missing hard coded biomes as regular biome files:
  - Land
  - Dungeon

Also added them back as hard coded fallbacks in biomes.go

…idual biomes to /empty

- Added defensive nil checks in mapper.go before calling biome methods
  - Ensured default biome always exists after LoadBiomeDataFiles() is
called
  - Added warning log when a requested biome is not found, showing biome
name, room ID, and zone
  - Improved biome fallback logic to prevent nil pointer dereferences
  - Added mudlog import to rooms.go for biome warning messages

- Added validateRoomBiomes() function in mapper that checks all rooms
during PreCacheMaps()
  - Logs warnings at startup for rooms without biomes (when zone also
has no default)
  - Logs warnings for rooms referencing non-existent biomes
  - Provides summary count of missing and invalid biome references