[roll] Roll fuchsia [ffx] Fix duplicate error formatting in SSH/target

Refactor error definitions in ffx_ssh and ffx_target to
remove inner error interpolation from their Display format.
This prevents duplicate error messages when formatting the error chain.

Also make FfxTargetCrateError::Fallback transparent to remove the
Temporary fallback error prefix, and clean up redundant wrapping in
SshConnector::connect_via_fdomain.

Before with ffx target status and a bad ssh key:

```
Diagnostics failed: Temporary fallback error: ControlMaster management error: Error spawning ssh control master: failed to start: permission denied: ControlMaster management error: Error spawning ssh control master: failed to start: permission denied: Error spawning ssh control master: failed to start: permission denied: failed to start: permission denied: permission denied
```

After:

```
Diagnostics failed: ControlMaster management error: Error spawning ssh control master: failed to start: permission denied
```

Original-Original-Bug: 424595846
Test: ffx_ssh_lib_test, ffx_target_lib_test, ffx_command_error_lib_test
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1661177
Original-Original-Revision: f43c8249b7d232ae345d18132fd82ac7cb19a86f
GitOrigin-RevId: 83f8f640c527d2c0ae405dfdb60d5290cb0f2d83
Change-Id: I76b644dfd07d777874a960908f1e5b76831f52a4
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1661440
Cr-Commit-Position: refs/heads/main@{#194942}