docs: fix obvious pre-existing Sphinx build warnings

Clears 6 of the 10 make-html warnings (none were from the httpx/migration work):
- get_channel: indent wrapped bullet continuations to the bullet-text column and add a trailing blank line so the time / last_modified "Examples" lists parse as RST instead of "bullet list ends without a blank line".
- get_monitoring_locations: make the two identical "list of codes" hyperlinks anonymous (__) to avoid a duplicate-target warning.
- conf.py: drop the deprecated sphinx_rtd_theme display_version option.
- add the referenced docs/source/_static/ directory (was configured in html_static_path but missing).
Remaining warnings (left as out of scope): the legacy NWIS_Metadata autodoc duplicate and the intentional !pip cells in WaterData_demo.

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

Author: thodson-usgs

dataretrieval/waterdata/api.py

@@ -554,11 +554,11 @@ def get_monitoring_locations(
     county_code : string or iterable of strings, optional
         The code for the county or county equivalent (parish, borough, etc.) in which
         the monitoring location is located. A `list of codes
-        <https://help.waterdata.usgs.gov/code/county_query?fmt=html>`_ is available.
+        <https://help.waterdata.usgs.gov/code/county_query?fmt=html>`__ is available.
     county_name : string or iterable of strings, optional
         The name of the county or county equivalent (parish, borough, etc.) in which
         the monitoring location is located. A `list of codes
-        <https://help.waterdata.usgs.gov/code/county_query?fmt=html>`_ is available.
+        <https://help.waterdata.usgs.gov/code/county_query?fmt=html>`__ is available.
     minor_civil_division_code : string or iterable of strings, optional
         Codes for primary governmental or administrative divisions of the county or
         county equivalent in which the monitoring location is located.
@@ -2751,9 +2751,10 @@ def get_channel(
             * A date-time: "2018-02-12T23:20:50Z"
             * A bounded interval: "2018-02-12T00:00:00Z/2018-03-18T12:31:12Z"
             * Half-bounded intervals: "2018-02-12T00:00:00Z/.." or
-            "../2018-03-18T12:31:12Z"
-            * Duration objects: "P1M" for data from the past month or "PT36H" for
-            the last 36 hours
+              "../2018-03-18T12:31:12Z"
+            * Duration objects: "P1M" for data from the past month or "PT36H"
+              for the last 36 hours
+
     channel_name : string or iterable of strings, optional
         The channel name.
     channel_flow : string or iterable of strings, optional
@@ -2799,9 +2800,9 @@ def get_channel(
             * A date-time: "2018-02-12T23:20:50Z"
             * A bounded interval: "2018-02-12T00:00:00Z/2018-03-18T12:31:12Z"
             * Half-bounded intervals: "2018-02-12T00:00:00Z/.." or
-            "../2018-03-18T12:31:12Z"
+              "../2018-03-18T12:31:12Z"
             * Duration objects: "P1M" for data from the past month or "PT36H" for the
-            last 36 hours
+              last 36 hours
 
         Only features that have a last_modified that intersects the value of
         datetime are selected.

docs/source/_static/.gitkeep

@@ -107,7 +107,6 @@
 
 html_theme_options = {
     "logo_only": False,
-    "display_version": True,
 }
 
 # Add any paths that contain custom static files (such as style sheets) here,