Replace typescript-private methods with native-private

• #3980 and #3983 covered class properties. Methods were never in scope, but crawlee/prefer-private-fields flags them too
• on master, there's 200+ private methods
• until we resolve this, we cannot make prefer-private-fields an error instead of warning

Spy seams

A test asserts a private method was called, so # breaks it outright rather than needing a rewrite.

• BrowserPool.executeHooks (8 sites), launchBrowser (2), overridePageClose, closeRetiredBrowserWithNoPages, closeInactiveRetiredBrowsers
• ConcurrencySystem.autoscale (9) — tests step the autoscaling loop by hand. Also does this.autoscale = this.autoscale.bind(this) in the constructor, which is illegal for a # method; it would have to become a private field holding an arrow function.
• SessionPool.ensureInitialized (3), createSession

Internals invoked directly

No public path to the behaviour under test.

• BasicCrawler.resolveRequestHandlerTimeoutMillis — currently the only handle on the 2^31-1 clamp, see #4043

• BasicCrawler.isTaskReadyFunction, runInStorageTransaction, isAllowedBasedOnRobotsTxtFile (2)

• HttpCrawler.encodeResponse (2)

• ImpitHttpClient.getClient (4) — asserts per-proxy client caching

• BrowserLauncher.getTypicalChromeExecutablePath (3)

• StagehandController.waitForStagehandToRegisterPage (2)

• Dataset.bufferedJournalEntries / KeyValueStore.bufferedJournalEntries

• Related: #3108, #3980, #3983