[SP-8499] Introduce always step

[msx2]

Introduces a new always DSL instruction that runs a step unconditionally at the end of the operation pipeline — regardless of whether prior steps succeeded, failed, or halted early via finish! or finish_if DSL.

How it works

always steps are declared after all regular instructions and execute even when the normal break condition (failure or early finish) would have stopped execution. Inside an always step, result.success? and result.failure? reflect the final state of the operation, allowing conditional logic based on outcome.

step :build
step :charge
step :send_confirmation
always :audit_log
always :cleanup

Placement rules enforced at class load time

• always steps must appear after all other instructions at the top level of the operation.
• Once an always is declared, only further always steps may follow — any other instruction (step, operation, transaction, within, etc.) raises an ArgumentError at class load time.
• always cannot be used inside blocks (transaction do, within do, success do, validate do). Doing so raises an ArgumentError at class load time.