feat(tempo): support machine-token payments

[mpp-agricola]

Motivation

Propagate feat(tempo): support machine-token payments from wevm/mppx#784 to tempoxyz/mpp-rs. The Agricola ticket #162 records the target decision and remediation lifecycle.

Summary

• Ports the behavior introduced by wevm/mppx#784.
• Adds target-native implementation and regression coverage.
• Links the change to the Agricola ticket #162.

Key design considerations

• Pins the port to wevm/mppx@61f847e8621b and tempoxyz/mpp-rs@8afed36e201b.
• Favors the target SDK's public API and conventions over source-language structure.
• Uses the stable agricola/mppx-784 automation branch.
• Remains a draft until a maintainer reviews the generated changes.

[gakonst]

Closing as superseded by #385, which landed the maintained machine-token charge implementation on current main. This generated port targets the pre-#385 checkpoint, overlaps the same client/protocol/server surfaces, and is now conflicting; #387 builds the session-settlement follow-on on top of #385.