```python
def thaw_row(row: str, steps: int) -> str:
    if not isinstance(row, str) or not row:
        raise ValueError("Row must be a non-empty string.")
    if not all(c in "#." for c in row):
        raise ValueError("Row can only contain '#' and '.' characters.")
    if not isinstance(steps, int) or steps < 0:
        raise ValueError("Steps must be a non-negative integer.")

    cells = list(row)
    for _ in range(steps):
        new_cells = cells[:]
        for i in range(len(cells)):
            if (i == 0 or cells[i - 1] == ".") and cells[i] == "#":
                new_cells[i] = "."
            elif (i == len(cells) - 1 or cells[i + 1] == ".") and cells[i] == "#":
                new_cells[i] = "."
        cells = new_cells

    return "".join(cells)
```