Bump declared Python floor to 3.9 to match CI

CI's matrix already tests only Python 3.9 / 3.13 / 3.14 (and the
waterdata test module skips itself on <3.10), but pyproject.toml still
declared requires-python = ">=3.8" and ruff was targeting py38. Bring
the manifest in line with reality:

- requires-python = ">=3.9"
- [tool.ruff] target-version = "py39"

That unblocks col.removesuffix("Date") in attach_datetime_columns
(restored), and surfaces two pre-existing pyupgrade fixes that ruff now
applies under the py39 target:

- dataretrieval/waterdata/ratings.py: import Iterable from
  collections.abc instead of typing.
- dataretrieval/waterdata/utils.py: zoneinfo is stdlib on 3.9+, so the
  ZoneInfo import moves into the stdlib group.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thodson-usgs

dataretrieval/utils.py

@@ -150,7 +150,7 @@ def attach_datetime_columns(df):
     for col in df.columns:
         if not col.endswith("Date"):
             continue
-        prefix = col[: -len("Date")]
+        prefix = col.removesuffix("Date")
         target = prefix + "DateTime"
         if target in columns or target in new_columns:
             continue

dataretrieval/waterdata/ratings.py

@@ -14,7 +14,8 @@
 
 import logging
 import os
-from typing import Any, Iterable, Literal, get_args
+from collections.abc import Iterable
+from typing import Any, Literal, get_args
 
 import pandas as pd
 import requests

dataretrieval/waterdata/utils.py

@@ -6,10 +6,10 @@
 import re
 from datetime import datetime
 from typing import Any, get_args
+from zoneinfo import ZoneInfo
 
 import pandas as pd
 import requests
-from zoneinfo import ZoneInfo
 
 from dataretrieval import __version__
 from dataretrieval.utils import BaseMetadata

pyproject.toml

@@ -6,7 +6,7 @@ build-backend = "setuptools.build_meta"
 name = "dataretrieval"
 description = "Discover and retrieve water data from U.S. federal hydrologic web services."
 readme = "README.md"
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 keywords = ["USGS", "water data"]
 license = "CC0-1.0"
 license-files = ["LICENSE.md"]
@@ -63,7 +63,7 @@ repository = "https://github.com/DOI-USGS/dataretrieval-python.git"
 write_to = "dataretrieval/_version.py"
 
 [tool.ruff]
-target-version = "py38"
+target-version = "py39"
 extend-exclude = ["demos"]
 
 [tool.ruff.lint]