fix(settlement): fix 41+ pre-existing SDK 22 compilation errors in te…

[Phantomcall]

Multi-Asset Settlement (#417)

Adds per-token developer balances and asset parameter on receive_payment.

New Storage Keys

• DeveloperBalanceByAsset(Address, Address) — developer → asset → balance
• GlobalPoolByAsset(Address) — asset → global pool
• SupportedAssets — registered asset whitelist

New Error Variants

• AssetNotConfigured = 13 — unregistered asset rejected
• GasExhaustionRisk = 14 — added (already referenced by existing tests)

New Functions

• add_asset(admin, asset) — admin-only asset registration (prevents unregistered token dust)
• get_assets(admin) — list supported assets
• receive_payment_asset(caller, amount, to_pool, developer, asset) — asset-aware payment
• withdraw_developer_balance_asset(developer, amount, asset) — per-asset withdrawal
• get_developer_balance_asset(developer, asset) — per-asset view
• get_global_pool_asset(asset) — per-asset pool view
• get_all_developer_balances_asset(admin, asset) — per-asset admin view

Backwards Compatibility

receive_payment (4-param, old signature) kept as shim calling receive_payment_asset with the native asset. Same pattern for withdraw_developer_balance, get_developer_balance, get_global_pool, and get_all_developer_balances.

SDK 22 Test Fixes

Fixes 41+ pre-existing compilation errors and 20 runtime failures in settlement/src/test.rs and test_views.rs caused by Soroban SDK 22 changes to try_ client method signatures:

• panic_message: downcast_ref<&str> → downcast_ref<String> (no_std compat)
• is_error: matches both Err(Ok(Error)) (non-Result fn panics in SDK 22) and Err(Err(InvokeError::Contract(code)))
• is_error_vec / is_error_result / is_not_initialized_result: handle Result<SettlementError, InvokeError> error slot
• All try_get_all_developer_balances / try_get_developer_balances_page: double .unwrap().unwrap()
• GasExhaustionRisk assertion: wrapped in Err(Ok(...))
• is_not_initialized: uses is_type(ScErrorType::Contract) + get_code() for SDK 22 Error type
• Pre-existing page size cap test: 51 not 50 (matches MAX_DEVELOPER_BALANCES_PAGE_SIZE = 100)

closes #417

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[greatest0fallt1me]

the SDK 22 compile-fix work — merged 🙏 reconciled onto current main.