fix: use the same sorting key for in memory impl of stacks chain tip

[matteojug]

Description

Fix a difference between the in memory and pg implementation of get_stacks_chain_tip, follow up for the broken test after the fake (non) bump in #1271.

Changes

Bump fake and fix the in memory implementation of get_stacks_chain_tip to align it to the pg implementation, by changing the endianness of the stacks block hash used for tie breaking.

Testing Information

The "broken" test now passes, and add two test to compare the get chain tip between the pg and in memory stores.

Checklist:

• I have performed a self-review of my code
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[cylewitruk]

Nice catch!