Implement SDK balance display normaliser

[El-swaggerito]

Description

Difficulty: Hard

Type: Feature

Summary

Implement a balance display normaliser for SDK consumers.

Current Behaviour

Balances may be displayed inconsistently across wallet, payment, and vault features.

Expected Behaviour

The SDK should provide shared formatting and normalisation helpers for native and issued asset balances.

Suggested Implementation

Create balance types, normalisation utilities, formatting helpers, tests, and docs.

Files or Areas Likely Affected

• src/accounts/
• src/wallet/
• src/utils/
• src/types/
• tests/
• docs/

Acceptance Criteria

• Balance normaliser is implemented.
• Native and issued asset balances are supported.
• Formatting is consistent.
• Invalid or missing balance states are handled.
• Tests cover balance display cases.
• Docs explain formatting assumptions.

Additional Notes

This supports consistent app behaviour.