Function checked_div_python_scale 

pub fn checked_div_python_scale(a: Decimal, b: Decimal) -> Option<Decimal>

Divide with Python decimal’s scale rule.

Python defines an ideal exponent for division: exp(a) - exp(b), i.e. an ideal SCALE of scale(a) - scale(b). An exact quotient is reduced toward that scale but never below the scale exactness requires:

  0.00 / 4     ->  0.00     ideal 2, exact needs 0  -> 2
  7    / 2     ->  3.5      ideal 0, exact needs 1  -> 1
  1.00 / 2     ->  0.50     ideal 2, exact needs 1  -> 2
  1.000 / 8    ->  0.125    ideal 3, exact needs 3  -> 3

rust_decimal misses this in BOTH directions, so a pad-only fix would be half a fix:

• Under, on a zero dividend — the same zero shortcut behind add_python_scale. 0.00 / 4 gives 0, dropping the scale.
• Over, on an exact quotient — 7 / 2 gives 3.50, one trailing zero more than the ideal exponent allows.

So the quotient is stripped to its minimal form and then padded up to the ideal scale; the two steps together land on Python’s answer from either side. An inexact quotient (1 / 3) has no trailing zeros to strip and a scale far past the ideal, so both steps are no-ops and it is returned as rust_decimal computed it.

Returns None on divide-by-zero or overflow, matching Decimal::checked_div — BQL maps that to NULL rather than panicking.