Pre-fill BillingRequestInput from dto.Request before ModelPriceHelper,
so tiered_expr billing resolves param() from the structured request
instead of reading HTTP body (which is empty in channel-test context).
- attachTestBillingRequestInput: marshal dto.Request → RequestInput
- ResolveIncomingBillingExprRequestInput: early-return when pre-filled
- settleTestQuota / buildTestLogOther: align test settlement & logging
with production TryTieredSettle / InjectTieredBillingInfo paths
- Added support for tiered billing expressions in the billing system.
- Introduced new types and functions for handling billing expressions, including caching and execution.
- Updated existing billing logic to accommodate tiered billing scenarios.
- Enhanced request handling to support incoming billing expression requests.
- Added tests for tiered billing functionality to ensure correctness.
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