fix(sdk): enforce the native asset decimal limit

[s6pa1rta3n-lab]

Summary

Enforces the 7-decimal stroop limit (MAX_STROOPS_DECIMALS) for native assets during asset config validation while retaining the 18-decimal limit (MAX_TOKEN_DECIMALS) for SAC assets.

Closes #259

Stipulations & Acceptance Criteria Checklist

• Native assets reject decimals above seven (0-7 stroop limit).
• SAC assets retain existing token limit (0-18).
• Existing valid fixtures pass.
• Boundary unit tests added for both asset types (0, 7, 8, 18, 19, negative values).
• SDK tests and typecheck pass without regressions.

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC