Fix: Add public initializers for SavedFeed and SavedFeedPreferencesVe…

[P24L]

Problem

When working with saved feeds preferences, it's currently impossible to create instances of SavedFeed and SavedFeedPreferencesVersion2Definition without using JSON serialization workarounds. These structs only have Decodable initializers, which makes programmatic creation unnecessarily complex.

Solution

This PR adds public initializers for:

• AppBskyLexicon.Actor.SavedFeed
• AppBskyLexicon.Actor.SavedFeedPreferencesVersion2Definition

Changes

Added public initializers following ATProtoKit's strict guidelines:

• Proper documentation with triple slashes
• All parameters documented
• Follows the established code structure pattern

Testing

The initializers have been tested to ensure they create objects identical to those decoded from JSON responses.

Example Usage

// Before (workaround required)
let savedFeedDict: [String: Any] = [
    "id": UUID().uuidString,
    "type": "list",
    "pinned": true,
    "$type": "app.bsky.actor.defs#savedFeed",
    "value": listURI
]
let jsonData = try JSONSerialization.data(withJSONObject: savedFeedDict)
let savedFeed = try JSONDecoder().decode(SavedFeed.self, from: jsonData)

// After (with this PR)
let savedFeed = SavedFeed(
    feedID: UUID().uuidString,
    feedType: .list,
    value: listURI,
    isPinned: true
)

[MasterJ93]

Thanks for the PR. I'll go ahead and merge it now.