feat(manager): add receipts_auto_delete

[aasseman]

receipts_auto_delete is a function that deletes receipts that are older than the last RAV.

Had to hack a bit with the tests to reduce code duplication:

• Using a test matrix instead of cases in manager_create_multiple_rav_requests_all_valid_receipts_consecutive_timestamps. The tests will run with and without the "receipts auto delete" right before the 1st and 2nd RAV.
• To make sure that the right number of receipts gets deleted, I needed to access the private receipt_storage_adapter attribute of Manager. Since the tests were originally outside the Manager source file (integration tests), I created a test helper function in the Manager source file that exposes the private receipt_storage_adapter attribute.

Fixes #108

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Pull Request Test Coverage Report for Build 5511368234

• 9 of 10 (90.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.3%) to 85.117%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tap_core/src/tap_manager/manager.rs	9	10	90.0%
<!--	Total:	9	10	90.0%	-->

Totals
Change from base Build 5510645575:	1.3%
Covered Lines:	978
Relevant Lines:	1149

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[aasseman]

Rabased onto latest main. Now tests are less hacky thanks to #135

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[aasseman]

Rebased onto latest main

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