Validate CSV output schemas

Also moved code dir to src.
There are reasons to do standard things in standard ways. While it is
possible to get the `code/` directory to work, and recognize it as a
package path, this requires wrangling the pyproject.toml file.
Additionally, any import from the `code.something` path automatically
shadows the python stdlib `code` module. While it may not be necessary,
it still is good to not shadow standard library modules.

code/files.py

@@ -1,41 +0,0 @@
-import csv
-from pathlib import Path
-
-
-def filesize_csv(input_dir: Path, output_dir: Path) -> None:
-    output_file = output_dir / "files.csv"
-    with output_file.open("w") as fw:
-        writer = csv.writer(fw)
-        writer.writerow(["date", "filename", "mtime", "filesize"])
-
-        for j in input_dir.glob("*.json"):
-            p_date = j.stem
-            p_fname = j.name
-            stat = j.stat()
-            p_mtime = stat.st_mtime
-            p_size = stat.st_size
-            writer.writerow([p_date, p_fname, p_mtime, p_size])
-
-
-def ensure_dirs(input_dir: Path, output_dir: Path):
-    if not input_dir.is_dir():
-        raise ValueError
-    output_dir.mkdir(exist_ok=True, parents=True)
-
-
-def main(input: str, output: str) -> None:
-    input_dir = Path(input)
-    output_dir = Path(output)
-    ensure_dirs(input_dir, output_dir)
-    filesize_csv(input_dir, output_dir)
-
-
-if __name__ == "__main__":
-    import sys
-
-    if not len(sys.argv) == 3:
-        print("Please provide exactly one input directory and one output directory.")
-        sys.exit(1)
-    inp = sys.argv[1]
-    out = sys.argv[2]
-    main(inp, out)