Minecart Trains Fork

Changes:

• fix: fix chained minecart unable to be pulled at low speed
• refactor: null type safety
• refactor: simplify the judgment of the middle cart
• build: update Fabric API version
• build: update Fabric loader version
• chore: update language file of en_us

Full Changelog: https://github.com/KSSJW/minecart-trains-fork/compare/2.5.0-alpha.4+26.2...2.5.0-beta.1+26.2