feat: bundler can have modules

[adhusson]

Modules are called using the bundler's new callModule(address module, bytes data) function. No onchain whitelist of module addresses is needed, and users should only approve modules they use.

When called, a bundler module receives the current initiator and the data argument. A module contract should inherit BaseMorphoBundlerModule and implement the internal function _morphoBundlerModuleCall. It is wrapped in an external function morphoBundlerModuleCall that checks the caller. So modules can trust that the initiator is correct.

Some alternatives:

• Remove BaseMorphoBundlerModule. Keep only the IMorphoBundlerModule interface and document that all implementations should check the caller. But it's more error-prone vs. the inheritance of BaseMorphoBundlerModule which is not heavy.
• Remove the caller check and the initiator argument, have modules call bundler.initiator() if they want to know the initiator. But it costs more gas.

Note: The signature of morphoBundlerModuleCall(address initiator, bytes calldata data) is 0xd26db89e and does not appear in 4byte.directory.