Remove src.lua imports

[Derpius]

Context

• Up until 74 - Add diff renderer and improve reporting #113, the require search paths were left as default, which meant we always had to require from the top of the lest package
• In that PR, we added ./src/lua/?.lua and ./src/lua/?/index.lua as search paths, but only shortened imports for files that were already touched

Scope

• Update all remaining require paths to drop src.lua.
• Remove the legacy ./?.lua search path

Acceptance Criteria

• Legacy search path is removed and there are no build errors