Add RecurringModule.transferPayer() to reassign payer

[lovesmilesmall-hue]

Summary

Implemented ransferPayer() - allows reassigning the payer of an existing recurring payment.

Changes

• Added ransferPayer(id, newPayer) to RecurringModule - Requires signing keypair (current payer) - Calls contract transfer_payer method - Added 2 unit tests

Closes #244

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[BigBen-7]

This PR currently has merge conflicts with main and was skipped during the batch merge pass. Please rebase/resolve conflicts and it can be merged.