Issues in End City Piece Generation

[maplelumi]

There are three issues in the end city generation:

1. Bridges are added to base instead of floor
   In finders.c -> genTower():

   Piece *bridge = addEndCityPiece(env, base, brot,
       binfo[i][1], binfo[i][2], binfo[i][3], BRIDGE_END);

This incorrectly attaches bridges to base. They should be attached to floor.

2. End ship assigned to base incorrectly
   In finders.c -> genBridge():

   base = addEndCityPiece(env, base, rot, x, y, z, END_SHIP); 

This modifies base. The final BRIDGE_END in genBridge should attach to the last BRIDGE_PIECE or stair, not the ship.

3. Depth type is too small
   In finders.h -> STRUCT(Piece): int8_t depth;
   In end city generation, depth is set using int gendepth = next(env->rng, 32); in genPiecesRecusively(). Using int32_t prevents overflow.

Example: Seed 155040604429240, Chunk (122, 80) generates an end city where these issues are observed.