refactor(client): Build each service once in the initializer

[abelonogov-ld]

LDClient.init builds the event reporter and the flag synchronizer, throws both away, and builds them again a few lines later — the second time with a callback that reports back to the client.

The duplication is not an oversight. Naming an instance method is an implicit reference to self, which Swift forbids until every stored property has a value, so neither callback could be given on the first pass. The workaround has been there since 2019. It is also the thing reviewers keep tripping over in the event-durability stack, so this lands on its own, ahead of it.

What changes

Each service is built once.

Event reporter. Its callback only ever logged, so it does not need a client at all. onEventSyncComplete becomes a static over an OSLog captured before the first assignment, and the reporter gets it at construction.

Flag synchronizer. Its callback genuinely reports to the client, so LDFlagSynchronizing makes onSyncComplete settable and the initializer assigns it once self is usable. The two other places that build a synchronizer are past initialization and still pass it at construction, so that path is unchanged.

Mock factory. onFlagSyncComplete now reads back from the synchronizer it made rather than from the factory call, so it sees the callback whichever way it arrived.

Not changed

connectionInformation is still assigned twice, for the same reason. It is a larger untangling and does not block anything, so it stays for now.

Verification

• 684 tests pass on iOS; macOS and tvOS build.
• Two new tests pin the behaviour: each service is built exactly once, and the synchronizer is told where to report. Both fail if the second construction is put back.
• No new SwiftLint violations. The three pre-existing LDClient.swift ones improve: initializer body 63 → 60 lines, class body 589 → 587.

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Note

Overview
LDClient initialization no longer constructs the event reporter and flag synchronizer twice. The duplicate build existed because sync-complete callbacks needed self before stored properties were fully initialized.

For the event reporter, sync completion only logged, so onEventSyncComplete becomes a static logEventSyncComplete that takes an OSLog captured at construction—no client reference required.

For the flag synchronizer, LDFlagSynchronizing now exposes a settable onSyncComplete; the initializer assigns onFlagSyncComplete once self is usable. Other code paths that create a synchronizer after init can still pass the callback at construction.

Tests and mocks track the new wiring: mocks gain onSyncComplete, the test factory records the built synchronizer and reads the callback from it, and LDClientSpec asserts each service is built exactly once and the synchronizer gets a non-nil reporter. DiagnosticReporterSpec adds an NSLock around captured diagnostic events to avoid races when retries append while the test thread is dequeuing.

^{Reviewed by Cursor Bugbot for commit 3b109a8. Bugbot is set up for automated code reviews on this repo. Configure here.}

Also: a pre-existing test flake

DiagnosticReporterSpec.testRetries occasionally failed under load with a leftover event. The mock answers a publish and its retry back to back on the reporter's queue, so the second append could land while the test thread was removing from the same unsynchronized array. The events are now taken under a lock. Test-only; 10 consecutive full-suite runs (8,240 tests) passed with it.