Non-integer PLACE rule position values break scale continuity / cause binder errors depending on layer type

Environment: ggsql-duckdb v0.3.2 and v0.4.1, DuckDB v1.5.3 and v1.5.4
Symptom A — Binder error with histogram:

SELECT CAST(20 + 40 * random() AS DOUBLE) AS value
FROM range(500)
VISUALISE value AS x
DRAW histogram
PLACE rule
  SETTING x => 44.4

Binder Error: No function matches the given name and argument types '-(VARCHAR, DECIMAL(12,10))'
LINE 1: ...GROUP BY (GREATEST(0, CEIL(("__ggsql_aes_pos1__" - 20.0171901952 + 1.3783433384 * 0.5) / 1.3783433384) -...

Symptom B — Silent scale-type flip (continuous → discrete) with point:

SELECT
    CAST(random() * 50 AS DOUBLE) AS x_val,
    CAST(random() * 50 AS DOUBLE) AS y_val
FROM range(50)
VISUALISE x_val AS x, y_val AS y
DRAW point
PLACE rule
  SETTING x => 21.5

No error is thrown, but the x-axis silently switches from a continuous numeric scale to a discrete categorical scale — every individual random value is rendered as its own axis category (long decimal tick labels), instead of a normal 0–50 continuous range.
Both symptoms disappear when the PLACE rule value is an integer:

-- Works, no error, x-axis stays continuous:
... PLACE rule SETTING x => 44   -- with histogram
... PLACE rule SETTING x => 22   -- with point

Root cause hypothesis: Supplying a non-integer literal to a PLACE rule position aesthetic appears to interfere with scale-type deduction for the whole visualisation. With histogram, this manifests as a binder error because the rule's non-integer value gets incorrectly folded into the histogram's own generated bin-index computation. With point, no computation is shared, so it doesn't error — but the scale still incorrectly gets deduced/coerced as discrete instead of continuous, likely due to the same underlying type-handling issue for non-integer literals in PLACE rule.
Expected: PLACE rule should accept any numeric literal (integer or decimal) without affecting the scale type of other layers or causing binder errors.
Workaround: round PLACE rule position values to the nearest integer.

Reproduce the histogram and point examples in ggsql-duckdb with decimal and integer PLACE rule values, then trace PLACE rule position handling and scale-type deduction in the Rust extension. Done means decimal numeric positions work for both layers, continuous scales remain continuous, and the histogram no longer produces a binder error.