DRY: Improvements to networking in PasskeyAuth actor

[Sajjon]

• Add makeUrl helper to create URLs in a DRY manner (using elegant KeyPath solution)
• Add get, getChallengeData, post using KeyPaths
• Add prepareAuthentication to check rate limit and if we are authenticating currently in a DRY manner
• Replace Int literal 429 with HTTPStatusCode TooManyRequests

[macroscopeapp]

Deduplicate networking and preflight checks in PasskeyAuth to DRY registration and login flows in PasskeyAuth.swift

Introduce shared helpers PasskeyAuth.prepareAuthentication, PasskeyAuth.performRequest, PasskeyAuth.get, PasskeyAuth.getChallengeData, PasskeyAuth.post, and PasskeyAuth.makeUrl; update PasskeyAuth.registerPasskey and PasskeyAuth.loginWithPasskey to use them; replace force-unwrapped UTF-8 for userID with Data(UUID().uuidString.utf8); add HTTPStatusCode.tooManyRequests handling.

📍Where to Start

Start with PasskeyAuth.performRequest and PasskeyAuth.post in PasskeyAuth.swift, then review their use in PasskeyAuth.registerPasskey and PasskeyAuth.loginWithPasskey.

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Macroscope summarized 154e89b.