Add test for recurring links and clean up method of retrieving recurring

[eileenmcnaughton]

Overview

This helps address blockers on #18787 and #18196 by

1. adding a preliminary unit test and
2. cleaning up the processor loading (for Always use cancelSubscription form for cancelling recurring contributions #18196 there is some code around this but the reason for the change there is not clear & it's it some code that needn't apply since we just want the object, we are not checking for capabilities )

Before

• No test
• convoluted method of loading the processor object goes through complex code that doesn't add anything here

After

• test to prevent behaviour change
• we use our preferred method to just load the object - however, I felt I had to improve the caching in it a bit, along with a couple of NFC changes

Technical Details

Comments

[civibot]

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[eileenmcnaughton]

This IF can go as it is always true & would be removed in a follow up PR

[eileenmcnaughton]

test this please

[eileenmcnaughton]

unrelated fail