Add renderer experiments and C-ROM visibility guard

[sabino]

Summary

• add named renderer experiment targets for focused ROM builds
• keep the texture-column simple-map experiment within the 1 MiB visible C-ROM window by using the reduced E1M1 sprite set and disabling ceiling perspective
• add a simple enemy visibility probe that fails when live imp/corpse tiles exceed the visible C-ROM tile range

Verification

• python3 -m py_compile tools/*.py
• make experiment-probes EXPERIMENT=texture_columns DOOM_IWAD=/home/sabino/Downloads/Doom1.WAD
• make experiment-cart EXPERIMENT=texture_columns DOOM_IWAD=/home/sabino/Downloads/Doom1.WAD
• git diff --check

Notes

• local manual GnGeo test confirmed the upper-right simple-map imp is visible again