fix: tighten decimal regex and fall through on unknown duration unit

Two nits from PR review:

- decimal regex 'decimal128?' made only the trailing 8 optional, so it
  matched the non-existent 'decimal12' form. Changed to
  'decimal(?:128|256)?' to accept decimal, decimal128, or decimal256.

- _ARROW_UNIT_TO_IBIS.get(..., 's') silently mapped any unrecognised
  duration unit (e.g. duration[foo]) to Interval(s). Now returns None
  so the caller falls through to the Postgres parser / String fallback.

Author: eddietejeda

src/ibis_hotdata/types.py

@@ -42,7 +42,7 @@
 # embedded parameters (unit, timezone, precision, value type, …).
 _TIMESTAMP_RE = re.compile(r"^timestamp\[(\w+)(?:,\s*tz=(.+))?\]$", re.IGNORECASE)
 _DURATION_RE = re.compile(r"^duration\[(\w+)\]$", re.IGNORECASE)
-_DECIMAL_RE = re.compile(r"^decimal128?\((\d+),\s*(\d+)\)$", re.IGNORECASE)
+_DECIMAL_RE = re.compile(r"^decimal(?:128|256)?\((\d+),\s*(\d+)\)$", re.IGNORECASE)
 _LIST_RE = re.compile(r"^(?:large_)?list<item:\s*(.+)>$", re.IGNORECASE)
 
 # Map Arrow time-unit strings to Ibis IntervalUnit strings and Timestamp scales.
@@ -79,7 +79,9 @@ def _parse_parametric_arrow_type(raw: str, *, nullable: bool) -> dt.DataType | N
 
     m = _DURATION_RE.match(raw)
     if m:
-        unit = _ARROW_UNIT_TO_IBIS.get(m.group(1).lower(), "s")
+        unit = _ARROW_UNIT_TO_IBIS.get(m.group(1).lower())
+        if unit is None:
+            return None  # unrecognised unit — fall through to Postgres parser / String fallback
         return dt.Interval(unit=unit, nullable=nullable)
 
     m = _DECIMAL_RE.match(raw)

tests/test_hotdata_types.py

@@ -113,13 +113,22 @@ def test_dtype_from_hotdata_arrow_duration(sql_type, expected_unit):
     assert out.nullable is False
 
 
+def test_dtype_from_hotdata_arrow_duration_unknown_unit_falls_back():
+    # An unrecognised duration unit should not silently map to seconds;
+    # it falls through to the Postgres parser (which returns Unknown) or String fallback.
+    out = dtype_from_hotdata_sql_type("duration[foo]", nullable=True)
+    assert not isinstance(out, dt.Interval)  # must not produce a valid Interval
+
+
 @pytest.mark.parametrize(
     ("sql_type", "expected_precision", "expected_scale"),
     [
         ("decimal128(10, 3)", 10, 3),
         ("decimal128(38, 0)", 38, 0),
+        ("decimal256(76, 38)", 76, 38),
         ("decimal(5, 2)", 5, 2),
         ("DECIMAL128(18, 6)", 18, 6),
+        # decimal12 is NOT a valid form — should not be matched by the decimal regex
     ],
 )
 def test_dtype_from_hotdata_arrow_decimal(sql_type, expected_precision, expected_scale):
@@ -150,3 +159,10 @@ def test_dtype_from_hotdata_arrow_list(sql_type, expected_value_cls, expected_it
     assert isinstance(out.value_type, expected_value_cls)
     assert out.value_type.nullable is expected_item_nullable
     assert out.nullable is True
+
+
+def test_dtype_from_hotdata_arrow_decimal12_not_matched():
+    # "decimal12" (only the trailing 8 made optional) must NOT match the decimal regex.
+    # The Postgres parser handles bare "decimal" forms; decimal12 is not a real type.
+    out = dtype_from_hotdata_sql_type("decimal12(10, 3)", nullable=True)
+    assert not isinstance(out, dt.Decimal)  # falls through to Unknown or String