Benchmark memory footprint during tests

### Description

Use [`SentrySystemWrapper.memoryFootprintBytes`](https://github.com/getsentry/sentry-cocoa/blob/2405ba598c9bae766901b68fd3cf1a9c5dca97af/Sources/Sentry/SentrySystemWrapper.mm#L7) to benchmark the memory footprint similar to what we do to [benchmark the CPU overhead ](https://github.com/getsentry/sentry-cocoa/blob/2405ba598c9bae766901b68fd3cf1a9c5dca97af/.github/workflows/benchmarking.yml#L77-L80). That approach notifies us about potential memory leaks anywhere in the SDK.

### Option discarded

[FBRetainCycleDetector](https://github.com/facebook/FBRetainCycleDetector) doesn't seem like a good option, as the last release for it was on November 2017, and we have to specify which objects we think could have retain cycles.