rusty-gd: Changes to make the HCI inquiry test pass

These include:

Writing count fields
Correct parsing of vectors
Using the correct offset when parsing struct fields

P.S. Also fixes the tokio panic caused by missing handling of the else
branch in the snoop HAL.

Bug: 171749953
Tag: #gd-refactor
Test: gd/cert/run --rhost DirectHciTest:test_inquiry_from_dut

Change-Id: I4bb884369d9d811c906e271c29460a3eb134a727