models: Add optional file name to SSUSI coeffs

Adds the option to pass a different file name to the SSUSI model
coefficient reader. Makes it consistent with the ZP2008 interface,
although it should not be necessary because there are already other ways
to pass custom coefficients.

src/eppaurora/models/ssusiq2023.py

@@ -42,19 +42,24 @@ def _interp(ds, method="linear", method_non_numeric="nearest", **kwargs):
 	return xr.merge([ds_n, ds_nn], join="left")
 
 
-def ssusiq2023_coeffs():
+def ssusiq2023_coeffs(file=None):
 	"""SSUSI ionization rate model coefficients
 
 	Returns the fitted ionization rate model coefficents as
 	read from the coefficient netcdf file.
 
+	Parameters
+	----------
+	file: str, optional
+		The coefficient file, defaults to the packaged coefficients.
+
 	Returns
 	-------
 	coeffs: `xarray.Dataset`
 		The default fitted model coefficients as read from the file.
 	"""
 	return xr.open_dataset(
-		COEFF_PATH, decode_times=False, engine="h5netcdf"
+		file or COEFF_PATH, decode_times=False, engine="h5netcdf"
 	)