feat(tempo): support machineUSD sessions

[decofe]

Summary

• bind machineUSD settlement routes into TIP-1034 descriptor salts while preserving the logical merchant and channel operator
• atomically settle escrow deltas through MachineUsdSwapper and persist adapter route metadata for reuse and indexing
• handle final-delta close as settle → convert → close, skip replay for fully settled channels, and reject refundable closes

Validation

• pnpm check
• pnpm check:types
• focused pure tests for route commitments, adapter calldata, cache scoping, and partial-route rejection

Full precompile E2E requires the companion MachineUsdSwapper and machineUSD reserve-whitelist changes; this PR intentionally rejects non-fully-consumed closes because machineUSD refunds are not currently recipient-policy compatible.

Prompted by: @gakonst

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/mppx@794

commit: 6bf8ae8

[parvahuja]

Superseded by #800 (refund-capable) and #801 (no-refund alternative), both using the one-flag merchant API and smoke-tested against their deployed contracts.

[parvahuja]

Superseded by #800 (refund-capable) and #801 (no-refund alternative), both using the one-flag merchant API and smoke-tested against their deployed contracts. This PR can be closed.