Fix memory leaks in tests

[mkurapov]

Context

When trying to debug remaining open handles in Jest tests reviewing this PR, I was unable to run jest tests serially via --runInBand/--detectOpenHandles because they were running out of memory due to a number of possible memory leaks.

There is an experimental jest argument: --detectLeaks that will fail a test if it detects that it is leaking memory:

max ~/interledger/rafiki/packages/backend [main] $ node ../../node_modules/jest/bin/jest.js --runInBand --detectLeaks --detectOpenHandles
{"level":30,"time":1707131063083,"pid":12851,"hostname":"max.local","msg":"creating knex"}
 FAIL   backend  src/open_payments/payment/outgoing/service.test.ts
  ● Test suite failed to run

    EXPERIMENTAL FEATURE!
    Your test suite is leaking memory. Please ensure all references are cleaned.

    There is a number of things that can leak memory:
      - Async operations that have not finished (e.g. fs.readFile).
      - Timers not properly mocked (e.g. setInterval, setTimeout).
      - Keeping references to the global scope.

      at onResult (node_modules/.pnpm/@jest+core@29.7.0/node_modules/@jest/core/build/TestScheduler.js:150:18)
      at node_modules/.pnpm/@jest+core@29.7.0/node_modules/@jest/core/build/TestScheduler.js:254:19
      at node_modules/.pnpm/emittery@0.13.1/node_modules/emittery/index.js:363:13
          at Array.map (<anonymous>)
      at Emittery.emit (node_modules/.pnpm/emittery@0.13.1/node_modules/emittery/index.js:361:23)

 FAIL   backend  src/open_payments/payment/combined/service.test.ts
  ● Test suite failed to run

    EXPERIMENTAL FEATURE!
    Your test suite is leaking memory. Please ensure all references are cleaned.

    There is a number of things that can leak memory:
      - Async operations that have not finished (e.g. fs.readFile).
      - Timers not properly mocked (e.g. setInterval, setTimeout).
      - Keeping references to the global scope.

      at onResult (node_modules/.pnpm/@jest+core@29.7.0/node_modules/@jest/core/build/TestScheduler.js:150:18)
      at node_modules/.pnpm/@jest+core@29.7.0/node_modules/@jest/core/build/TestScheduler.js:254:19
      at node_modules/.pnpm/emittery@0.13.1/node_modules/emittery/index.js:363:13
          at Array.map (<anonymous>)
      at Emittery.emit (node_modules/.pnpm/emittery@0.13.1/node_modules/emittery/index.js:361:23)
      
      
.... and so on      

This fails most of our tests due to several reasons.

It looks like the main culprit is the nock library:

• https://github.com/nock/nock?tab=readme-ov-file#memory-issues-with-jest
• Jest --detectLeaks reports memory leaks on nock.cleanAll() and nock.restore() nock/nock#2358

Some other culprits are the

• tigerbeetle testcontainer not being torn down properly after the test has been ran (related: Gracefully stop individual TB testcontainers #1094)