Refactor/migrate transactions viem

[Rav1Chauhan]

Addressed Issues:

Part of the phased migration from web3.js to viem.
Fixes #79

Screenshots/Recordings:

Not applicable — this PR modifies SDK-level transaction handling and does not introduce UI changes.

Additional Notes:

This PR migrates transaction preparation logic from web3.js to viem.

Changes included:

Replaced djed.methods(...).encodeABI() usage

Removed buildTx dependency

Introduced viem transaction configuration object

Used parseUnits for value handling

No removal of web3 dependency yet (to be handled in a later PR)

Checklist

• [x ] My PR addresses a single issue, fixes a single bug or makes a single improvement.
• [ x] My code follows the project's code style and conventions.
• If applicable, I have made corresponding changes or additions to the documentation.
• If applicable, I have made corresponding changes or additions to tests.
• [ x] My changes generate no new warnings or errors.
• [ x] I have joined the Stability Nexus's Discord server and I will share a link to this PR with the project maintainers there.
• [ x] I have read the Contribution Guidelines.
• [ x] Once I submit my PR, CodeRabbit AI will automatically review it and I will address CodeRabbit's comments.

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[Rav1Chauhan]

assign it to me .