fix(sdk-coin-polyx): fix address creation flow for Polyx

[nvrakesh06]

Summary

• Fix getWalletInitializationBuilder() in TransactionBuilderFactory to return a RegisterDidWithCDDBuilder instead of throwing NotImplementedError
• Override requiresWalletInitializationTransaction() in Polyx to return true, since Polymesh requires an on-chain DID registration (cddRegisterDidWithCdd) before an address can receive funds
• Add unit tests covering both new behaviors

Test plan

• Run BITGOJS_TEST_PASSWORD=test yarn run unit-test --scope @bitgo/sdk-coin-polyx — 104 tests pass
• Verify getWalletInitializationBuilder() returns a RegisterDidWithCDDBuilder instance
• Verify requiresWalletInitializationTransaction() returns true for both polyx and tpolyx

Ticket: CECHO-58

🤖 Generated with Claude Code

[linear]

CECHO-58 [Polyx] Fix the address creation flow