Fix OAuth token extraction from httr saved format

[TroyHernandez]

Summary

httr's oauth2.0_token saves tokens as a list with a hash key, but yt_oauth was using the list directly instead of extracting the Token2.0 object. This caused "attempt to apply non-function" errors when making API calls with a previously saved token.

The Problem

When a token is saved with saveRDS() and later loaded, httr wraps it in a list structure:

# Token gets saved as:
list("abc123hash" = <Token2.0 object>)

The existing code passed this list wrapper to options(google_token = ...), but API calls expect the actual Token object.

The Fix

Extract token[[1]] when the loaded object is a list wrapper rather than a Token object:

if (is.list(saved_token) && !inherits(saved_token, "Token")) {
  saved_token <- saved_token[[1]]
}

Test Plan

• Tested with saved OAuth tokens from multiple YouTube channels
• Verified token refresh works correctly
• Confirmed upload_video() and other API calls work with loaded tokens