[Whitelisted Caller] Upgrade Polkadot RC and system chains to 1.7.1

This is a referendum to upgrade Polkadot Relay Chain and Polkadot System Chains to the 1.7.1 Runtimes release.

The highlights of the 1.7.1 (and included 1.7.0) release are:

• Integrating "Empowered XCM Origins" features to System Chains,
• Adding Snowbridge V2 pallets, to enable Snowbridge V2 bridging,
• Upgrading to the latest Polkadot-SDK (2507) that comes with many fixes and enhancements.

For the full list of changes, please read the fellowship 1.7.0 release notes and 1.7.1 release notes.

If approved, it is scheduled to enact at block 27994000, estimated time 2025-09-30 10:42:01 (UTC).

Whitelist: https://collectives.subsquare.io/fellowship/referenda/402

🚨 Important note for Ecosystem builders: 🚨

In preparation for the upcoming Asset Hub Migration we changed the behavior of transfer_assets and (limited_)reserve_transfer_assets extrinsics to remove DOT/KSM support. You can find more information about what is changing, which SDK versions are affected, along with instructions on how to follow up in this guide.

We recommend that Parachains and dapp builders switch to using alternative extrinsics as instructed in the guide above, otherwise cross-chain transfers may start failing.