feat: update `Site.expandtemplates` to use the new API added in 1.24

Refactored `Site.expandtemplates` to use the updated API, addressing
deprecation warnings in recent MediaWiki versions.

The older API triggered the following warnings:

```
WARNING:mwclient.client:Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/postorius/lists/mediawiki-api-announce.lists.wikimedia.org/> for notice of API deprecations and breaking changes. Use [[Special:ApiFeatureUsage]] to see usage of deprecated features by your application.
WARNING:mwclient.client:The parameter "generatexml" has been deprecated.
Because "prop" was not specified, a legacy format has been used for the output. This format is deprecated, and in the future the new format will always be used.
```