[roll] Roll fuchsia [adb] Fix asan test flake in teardown observer

This change fixes a use-after-free flake in adb-test where the
ObserveTeardown callback in UsbAdbImpl was accessing the Adb
instance after it had been destroyed during test teardown.

To fix this:
1. Added a shared_ptr to a callback (`teardown_callback_`) in Adb.
2. In StartUsbAdbImpl, the ObserveTeardown lambda captures a copy of
   this shared_ptr instead of capturing `this`.
3. In the Adb destructor, we clear the callback in the shared state
   (`*teardown_callback_ = nullptr`).
4. When teardown completes, the lambda checks if the callback is still
   valid before executing it. This ensures we don't access the
   destroyed Adb instance.

Also fixed the teardown order in `AdbRealmTest::TearDown` to ensure
the realm is torn down before `AdbTest::TearDown` destroys the
FakeAdb instance.

Original-Bug: 500597818
Test: fx test adb-test
Multiply: adb-test
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1570481
Original-Revision: 8bd0e214e22d9b033edf396efdfa2b1868eb3c67
GitOrigin-RevId: e2b3cc8182538c0894a80d49f466772d0ba51026
Change-Id: If4eea64a244197862c19bd55d0b4e221a2aeef36