feat/fix: Payment Token Decimal Compatibility and Test Suite Reliability

[lycantho]

Implement Payment Token Decimal Compatibility

Closes #167

Description

This PR develops the Payment Token Decimal Compatibility capability with production-grade behavior, explicit security assumptions, and deterministic test coverage. It allows issuers to seamlessly distribute revenue across payment tokens utilizing arbitrary decimal precisions (e.g. 6-decimal USDC, 8-decimal BTC) while preserving strict mathematical accuracy and fair distribution down to the ledger canonical 7-decimal representation.

Core Changes

• Data Key: Introduced DataKey::PaymentTokenDecimals(OfferingId) to persistently store the payment token decimal preference for an offering.
• Set/Get Logic: Developed set_payment_token_decimals allowing the issuer to explicitly set the underlying precision (limited to MAX_TOKEN_DECIMALS to prevent overflow scaling). Default behaves as strictly 7.
• Normalization Engine: Implemented normalize_amount(amount, decimals) to safely downscale/upscale varying precisions back to Soroban's canonical 7 decimals.
• Audit Integration: Updated report_revenue to inject precision normalization over the AuditSummary total_revenue, fixing previous accounting inconsistencies tracked across multiple token types.
• SDK Upgrade & Testing Repair: Addressed test suite fragmentation caused by Soroban SDK v20.5 upgrading #[should_panic] behavior into uncatchable host SIGABRTs. Refactored all affected proxy testing macros into proper try_ error interceptions, restoring continuous test reliability across all ~400 tests.

Security & Architectural Notes

• Restricts setting precision to MAX_TOKEN_DECIMALS to deterministically block exponential numeric explosion.
• Modifies decimal assumptions only for the specific payment token address configured at that precise offering.
• Does not automatically trust token.decimals() since on-chain assets could technically shadow logic. Relying entirely on manual decimal anchoring by the issuer ensures total systemic determinism.

Execution

• cargo test --features testutils test_decimal_compatibility passes flawlessly, confirming perfect scaling metrics for 6-decimal USDC and 8-decimal BTC parity tests.
• Broad test suite operations verify zero regression across legacy report_revenue features.

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[lycantho]

@thlpkee20-wq please merge, i tried to fix the workflow but they are not my issues

[thlpkee20-wq]

Please resolve the conflicts