Add metadatabase URL override for CloudKit sync

[byMohamedali]

Summary

Adds an optional metadatabaseURL override to SQLiteData's CloudKit APIs so callers can choose where the CloudKit metadata database lives.

Changes

• Add metadatabaseURL: URL? = nil to:
  • SyncEngine.init(for:tables:privateTables:containerIdentifier:metadatabaseURL:defaultZone:startImmediately:delegate:logger:)
  • Database.attachMetadatabase(containerIdentifier:metadatabaseURL:)
• Preserve existing behavior when no override is provided.
• Create the parent directory of the resolved metadata URL instead of always creating Application Support.

Motivation

Some platforms, notably tvOS, may not allow the current hardcoded Application Support behavior for this metadata database. The main user database may already be configured to live somewhere else, but CloudKit setup still fails because the metadata store is not configurable.

This change keeps the default behavior intact for existing apps while allowing callers to explicitly provide a writable location when needed.

Example

let metadataURL = FileManager.default
  .urls(for: .cachesDirectory, in: .userDomainMask)
  .first?
  .appendingPathComponent(".SQLiteData.metadata.sqlite")

var configuration = Configuration()
configuration.prepareDatabase { db in
  try db.attachMetadatabase(metadatabaseURL: metadataURL)
}

let database = try SQLiteData.defaultDatabase(
  path: databaseURL.path,
  configuration: configuration
)

let syncEngine = try SyncEngine(
  for: database,
  privateTables: MyTable.self,
  metadatabaseURL: metadataURL
)

[mbrandonw]

Hi @byMohamedali, it's intended that the metadatabase is created right alongside wherever the user's database is. You can see that's done right here:

sqlite-data/Sources/SQLiteData/CloudKit/SyncEngine.swift

Lines 2139 to 2143 in 65502ac

	return
	databaseURL.deletingLastPathComponent().appending(
	component: ".\(databaseURL.deletingPathExtension().lastPathComponent)"
	)
	.appendingPathExtension("metadata\(containerIdentifier.map { "-\($0)" } ?? "").sqlite")

So I'm not sure why this would be needed. Are you positive that the metadatabase is always created in application support?