Doing an euclidean division on floats with the native operators is unreliable: because of IEEE-754 representation errors, `value1 % value2` can return a spurious remainder (e.g. `50.4 % 16.8 == 16.799999999999997` instead of 0.0) and `int(value1 / value2)` can truncate the quotient one step too low (e.g. `int(0.3 / 0.1) == 2` instead of 3). `float_div` returns the `(quotient, remainder)` pair free of those errors.

The key is to never run a lossy `%` or `//` on the raw floats. Instead both operands are first snapped onto the precision grid with `float_round` and then scaled to integers: since a grid-snapped value is a multiple of `rounding`, dividing it by `rounding` counts how many grid steps it spans. That division is still noisy (`4.35 / 0.05 == 86.99999999999999`), so the result is passed through `builtins.round` to coerce it to the exact integer step count. The euclidean division itself is then a plain integer `divmod`, which is exact, and the remainder is scaled back to real units. This is why the correction is applied to the inputs and not to the output: rounding the result of a native `%` would only round an already-corrupt value, and would still misreport the quotient in the corner cases the util exists to handle.

Dividing by `rounding` is meaningful for any precision, not only powers of ten: the grid step can be `0.05`, `0.25`, `0.5`, `0.03`, ... and `value / step` counts the steps in every case. This mirrors the normalize/denormalize scheme `float_round` already uses internally.

The util shares `float_round`'s inherent limitation: the scaled step count must stay representable as an exact `float` integer, so exactness is lost past ~2**53 grid steps (extreme magnitudes at a fine precision). This is the IEEE-754 double-precision ceiling and is well outside any realistic quantity or price range.

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Forward-Port-Of: odoo/odoo#280456
Forward-Port-Of: odoo/odoo#277160