fix: support viem auto-swap calls

[brendanjryan]

Motivation

viem@>=2.54 changed Tempo call builders to require a client-first call shape. The charge transfer path was updated in 0.8.3, but auto-swap still built the DEX buy call with the old single-argument shape.

Summary

• Added a client-aware DEX buy call builder for Tempo auto-swap.
• Hardened token metadata decimal handling for account balance display.
• Added coverage for viem client-first auto-swap builders and metadata decimal fallback.

Key design considerations

• Kept compatibility with both old and new Tempo call builder shapes.
• Matched the existing helper pattern already used for token balance and approve builders.
• Preserved the current balance display fallback behavior when token metadata is unavailable.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/mppx@606

commit: 58e5a0a