fix(wallets): prevent account-change listener leak on reconnect in XBullAdapter (closes #840)

[guptakumarranjeet150]

Summary

Closes #840

Fixes account-change listener leakage in by unsubscribing the previous registration before registering a new one during repeated invocations, ensuring at most one active listener is maintained with the wallet and preventing post-disconnect state mutation.

Key Changes

• Listener Teardown Guard ():
  • In , explicitly invokes and sets before re-registering with .
  • Mirrors behavior of sibling and prevents orphaned listener callbacks from mutating after .
• Unit Test Suite ():
  • Validates initial single registration upon .
  • Validates multiple sequential calls clean up prior listeners and leave strictly 1 live listener.
  • Validates cleans up the active listener and leaves 0 live listeners.
  • Validates account change propagation to registered handlers.

Verification

• bun test v1.4.0 (34cbb9a40): 4/4 unit tests passed 100% green.

[Kingsman-99]

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