Standardize CDP SQL numeric schemas

[LeeSee1999]

Fixes #45.

Summary

• Add shared cdpSqlNumberSchema and cdpSqlIntegerSchema helpers for CDP SQL aggregate responses.
• Update transfers aggregate result schemas to accept CDP stringified numerics while returning cache-safe JavaScript number values.
• Remove the local one-off total_amount conversion in bucketed transfer stats now that the result schema handles the coercion consistently.

Verification

• git diff --check
• pnpm exec prettier --check <changed transfer service files>
• pnpm --filter @x402scan/app types:check was attempted locally. It currently fails before a clean app check because the local checkout is missing generated Prisma/Next/workspace type artifacts and reports existing project-wide type errors outside this change. I filtered the output for the modified src/services/transfers paths and did not find errors from this patch.

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