Add support for all common Arrow type strings returned by Hotdata's
information_schema when tables are loaded from Parquet/Arrow sources.

Simple additions to _ARROW_TYPE_MAP:
- int8 → dt.Int8 (Postgres parser wrongly returns Int64 for "int8")
- halffloat → dt.Float16 (PyArrow's str() name for float16
- large_string → dt.String (PyArrow large-offset string variant)

New _parse_parametric_arrow_type() for types with embedded parameters:
- timestamp[us] / timestamp[us, tz=UTC] → dt.Timestamp(timezone=...)
- duration[ms] → dt.Interval(unit='ms')
- decimal128(10, 3) / decimal(5, 2) → dt.Decimal(precision, scale)
- list<item: T> / large_list<item: T> → dt.Array(T) (recursive)

Adds 27 new test cases covering all new patterns including timezone
variants, all 4 time units, case-insensitivity, and recursive list
element type resolution.
EOF
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Two bugs found by Codex review:

1. Timestamp scale was discarded: Arrow timestamp[ms] should map to
   dt.Timestamp(scale=3), not dt.Timestamp(). Add unit-to-scale mapping
   s=0, ms=3, us=6, ns=9, matching PyArrow convention.

2. Non-nullable list items mis-parsed: PyArrow emits
   'list<item: int32 not null>' for non-nullable item fields. Strip the
   ' not null' suffix and pass nullable=False to the recursive call so
   the element type is correctly typed instead of falling back to Unknown.

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.

Instead of constructing Ibis types directly (with hand-coded unit->scale
mappings etc.), resolve Arrow type strings to PyArrow types first and
convert via ibis.formats.pyarrow.PyArrowType.to_ibis().

- Replace _ARROW_TYPE_MAP (str -> Ibis class) with _PA_TYPE_MAP
  (str -> pa.DataType instance), covering all scalar types that can
  appear as list element types
- Merge _parse_parametric_arrow_type() into _pa_type_from_arrow_str()
  which returns a pa.DataType or None
- Remove _ARROW_UNIT_TO_IBIS and _ARROW_UNIT_TO_TIMESTAMP_SCALE —
  PyArrow encodes unit/scale semantics natively
- Fix decimal256: pa.decimal128 rejects precision > 38; fall back to
  pa.decimal256 for wider values
- dtype_from_hotdata_sql_type() simplified to: try Arrow path via
  PyArrow bridge, then Postgres parser, then String fallback

- backend.py: replace walrus-then-overwrite pattern with plain assignments
  in _to_catalog_db_tuple
- backend.py: getattr(self, '_http', None) is not None -> hasattr(self, '_http')
- backend.py: add explanatory comments to the silent pass in
  _resolve_database_connection_id and the no-op _register_in_memory_table
- http.py: replace magic HTTP status integers with http.HTTPStatus constants
- http.py: replace range(len(columns)) index loop with direct field iteration
- types.py: cache m.group(2) to avoid calling it twice
- Remove managed.py (single-constant module); inline 'public' directly at
  the two call sites in backend.py and http.py

- Correct ibis-framework version requirement to >=10,<11
- Document all connect() optional parameters with inline comments
- Add URL query string example with optional parameters
- Document schema-only create_table (empty table from schema)
- Document force=True on drop operations
- Note to_pyarrow_batches() downloads full result then splits locally
- Add in-memory tables (unsupported) and Arrow type mapping to feature table

- Change default schema public to main to match runtimedb DEFAULT_SCHEMA_NAME;
  runtimedb auto-inserts main into every managed database, so using public
  silently created a spurious empty main schema alongside the declared one
- Trim _IN_FLIGHT to {running} — runtimedb QueryRunStatus only emits
  running, succeeded, and failed; queued and pending are result statuses
- Update README examples to use main schema throughout