add buffer_geometry helper function to utils_geo module

[gboeing]

This new function offers users a small quality-of-life improvement for use cases like:

• modeling a buffered graph around some study area (e.g., Feature Request: Adding Buffer Zone Function to OSMnx #1072, deprecate buffer_dist and clean_periphery arguments #1044 (comment))
• retaining all edges that intersect a study area even if their endpoint nodes are all outside the study area (e.g., Feature request: truncate_by_nearest_edge while generating graph from point #1207)

For example, to download a graph within a 500 meter buffer of a city's boundaries:

import osmnx as ox
geom = ox.geocoder.geocode_to_gdf("Piedmont, CA, USA").iloc[0]["geometry"]
G = ox.graph.graph_from_polygon(ox.utils_geo.buffer_geometry(geom, 500), network_type="drive")

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.31%. Comparing base (94b7e73) to head (95846f2).
Report is 4 commits behind head on main.

Additional details and impacted files

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  Coverage   98.31%   98.31%           
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  Files          24       24           
  Lines        2369     2374    +5     
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+ Hits         2329     2334    +5     
  Misses         40       40           

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