[deps] Remove need for polyfill for Buffer.from

[gregnazario]

Description

Test Plan

Related Links

Checklist

• Have you ran pnpm fmt?
• Have you updated the CHANGELOG.md?

[Copilot]

Pull request overview

This PR removes reliance on Buffer.from (and associated polyfills) by switching string-to-bytes serialization to a shared TextEncoder and base64/base64url conversions to js-base64 utilities.

Changes:

• Introduces a shared TEXT_ENCODER constant and updates internal code paths to use it instead of Buffer.from(..., "utf8").
• Replaces base64url encoding/decoding that previously used Buffer with js-base64 (Base64.fromUint8Array(..., true) / Base64.toUint8Array(...)).
• Updates unit/e2e tests to use the new encoding utilities.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/unit/address.test.ts	Updates seeds to use TEXT_ENCODER.encode(...) instead of Buffer.from.
tests/e2e/transaction/signTransaction.test.ts	Switches base64url challenge encoding from Buffer helpers to js-base64.
tests/e2e/transaction/helper.ts	Replaces exported base64url helper implementation with js-base64.
src/utils/helpers.ts	Replaces Buffer base64 decode with js-base64 decode utilities.
src/utils/const.ts	Adds shared TEXT_ENCODER constant.
src/transactions/transactionBuilder/remoteAbi.ts	Uses shared TEXT_ENCODER import instead of a local instance.
src/core/account/utils/address.ts	Replaces Buffer.from(seed, "utf8") with TEXT_ENCODER.encode(seed).
src/bcs/serializer.ts	Moves string serialization to shared TEXT_ENCODER import.
package.json	No functional change (format-only).

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