web-wallet: Review and Refactor `amount` Logic in Migrate Flow

[nortonandreev]

Description

The logic around the amount property in the Migrate flow requires a thorough review and refactor. Key issues include:

1. Use of bigint for Operations

   • Ensure that all operations involving amount use bigint for consistency and to prevent potential precision issues.

2. Repetition in String Handling Logic

   • The logic for handling amount as a string and displaying it appears to be repeated in multiple places. This should be centralized to avoid duplication and improve maintainability.

Example:

[nortonandreev]

Update – this has already been refactored. Checking for proper usage of bigint values is still needed tho.