Add outflow_source option to pi() (cape_star vs cape_env) and docume…

[dgilford]

This pull request introduces a new configuration option for the pi function in the tcpyPI package, allowing users to choose how the outflow temperature and level are defined when calculating tropical cyclone potential intensity (PI). The changes add the outflow_source parameter (with options "cape_star" and "cape_env"), update documentation and sample code to reflect this, and include new tests to ensure correct behavior.

Key changes:

New Feature: Outflow Source Selection

• Added an outflow_source parameter to the pi function, allowing users to select whether the outflow temperature/level is defined using the saturated CAPE* calculation ("cape_star", default) or the environmental CAPE calculation ("cape_env"). The implementation ensures the correct values are used based on the user's choice. [1] [2] [3]

Documentation Updates

• Expanded the README.md to document the new outflow_source option and other sensitivity/configuration options, including usage examples.
• Updated docstrings in src/tcpyPI/pi.py to include the new parameter and clarify its behavior. [1] [2]

API and Sample Code Adjustments

• Modified the run_sample_dataset function in run_sample.py to accept the outflow_source parameter and pass it through to the pi function, updating both the function signature and docstring. [1] [2] [3]

Testing

• Added a new test module tests/test_outflow_source.py to verify that both outflow_source modes produce valid results and that invalid values raise appropriate errors.