test: add message builder fromBroadcastString() test cases

[bhavidhingra]

This pull request adds comprehensive tests for the fromBroadcastString method in message builder factories for multiple coins (ETH, ADA, SOL), ensuring that broadcastable strings are parsed correctly and return the appropriate builder types. Each test verifies that the parsed message payload, signers, destination addresses, amounts, and signatures match expected values, improving reliability and coverage for message serialization and deserialization.

Message builder factory broadcast string parsing tests:

• Added a test for EIP-191 messages to validate parsing of broadcastable strings, checking payload, signer address, destination address, amount, signature, and public key. (modules/abstract-eth/test/unit/messages/eip191/eip191MessageBuilder.ts)
• Added a test for CIP8 ADA messages to validate parsing of broadcastable strings, checking payload, signer address, destination address, amount, signature, public key, and COSE encoding outputs. (modules/sdk-coin-ada/test/unit/messages/cip8/cip8MessageBuilder.ts)
• Added a test for Solana simple messages to validate parsing of broadcastable strings, checking payload, signer address, destination address, amount, signature in both base58 and hex formats, and public key. (modules/sdk-coin-sol/test/unit/messages/simpleMessageBuilder.ts)

Test setup improvements:

• Updated imports in test files to include MessageBuilderFactory and other required utilities to support the new tests. (modules/abstract-eth/test/unit/messages/eip191/eip191MessageBuilder.ts, modules/sdk-coin-ada/test/unit/messages/cip8/cip8MessageBuilder.ts, modules/sdk-coin-sol/test/unit/messages/simpleMessageBuilder.ts) [1] [2] [3]

Example usage addition:

• Added an example script to demonstrate how to obtain an access token for a BitGo account using the SDK. (examples/ts/access-token.ts)

TICKET: COIN-5225