Function emit_tsconfig_with_source_maps 

pub fn emit_tsconfig_with_source_maps() -> String

The bynkc test --coverage variant (#854): the same config with sourceMap enabled, so tsc emits the .js.maps the coverage remap consumes (hop 1, .js → emitted .ts). Kept coverage-only rather than folded into the default so a normal bynkc test / deployment tsc run ships no .js.maps. The runner overwrites the default out/tsconfig.json with this before tsc.