Incorrect line prefixing

The way you're prefixing assumes that stdout/stderr "data" events always emit entire lines, which can be demonstrated to be false by using the `@biomejs/biome` npm package's `biome check` command. Example output: ``` biome The number of diagnostics exceeds the number allowed by Biome. biome Diagnostics not shown: 230. biome Checked 179 files in 249ms. No fixes applied. biome Found 249 errors. biome chec biome k ━━━━━━━━━━━━━━━━━━━━ biome ━━━━━━━━━━━━━━━ biome ━━━━━━━━━━━━ biome ━━━━━━━━━━━━━━━━━━ biome ━━━━━━━━━━━━━ biome ━━━ biome ━━━━━━━━━━━━━ biome × Some erro biome rs were emitted while running checks. ```