Replace urllib.request with urllib3 to support WebAssembly

[rpwagner]

As discussed in #2514, urllib.request is not supported in WebAssembly. This replaces urllib.request where needed with urllib3 which does work with WebAssembly. I've tried to keep the code changes to a minimum and to reuse existing semantic patterns.

The linter did introduce new lines in one of the imports. I found it odd but left it in place.

Rationale

This enables the use of Cartopy is Pyodide and JupyterLite. Without it, downloading of shape files, etc., fail. See #2514.

Implications

I've run the unit tests and nothing new fails. It's also been tested in JupyterLite and works. There is a chance that the download code path hasn't been fully tested and something may still need to be changed to support urllib3.

This also introduces a new dependency, even though urllib3 is widely available. It is also an existing package in Pyodide.

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