feat: added migration & ownable

[leohhhn]

Description

This PR introduces ownership & realm migration functionality to the chess package, and addresses issue #56.

This PR also introduces an init function to the Chess realm, setting the realm owner to its deployer keypair upon deployment. The following functionality is added:

Ownership functionality:

• owner variable is added to realm state,
• ownership can be transferred to different address by current owner,
• calling isOwner() will check if the caller is owner and will panic if the caller is not the owner,

Migration functionality:

• migrateTo variable added to represent the path of new deployment of realm
• migrated bool added to indicate if a migration has happened before
• Migrate function to allow migrating, only callable by current owner of realm
• All exported functions are uncallable if realm has migrated - check done by checkMigrated

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