Fix IOS remote file copy credentials and report device copy errors

[mattmiller87]

Summary

FTP transfers to Cisco IOS devices never authenticated. FileCopyModel.__post_init__ strips credentials out of the download URL (pyntc/utils/models.py:88-90), and the IOS driver sent that stripped URL to the device. It relied on answering Source username and Password prompts instead. IOS does not issue those prompts for copy ftp:. The device attempted an anonymous login, the server refused it, and the transfer failed in under half a second.

The failure was reported through a Nautobot OS upgrade workflow, which surfaced this:

FileTransferError:
An error occurred during transfer. Please make sure the local file exists and
that appropriate permissions are set on the remote device.

What Changed

Two commits, because these are two separate defects:

1. Fix IOS remote file copy dropping URL credentials is the reported bug.
2. Report the device error when a remote file copy fails improved logging across four drivers.

Changes by driver

Repurposed existing methods to make all drivers consistent

Element	Copied from
_netloc, _source_path, _build_url_copy_command_*	nxos_device.py:413-438
for/else guard on the prompt loop	asa_device.py:1110-1123
Error carrying the device output	eos_device.py:633-637
Token masking	jnpr_device.py:1829
or "" on the prompt answers	nxos_device.py:596-597

ios_device.py gets the credential routing, the prompt-answer defaults, the error detail and the loop guard.

nxos_device.py, asa_device.py and iosxr_device.py get the error detail only, plus the loop guard where they lacked one. ASA and IOS-XR already logged the device output and then threw it away at the exception.

Testing

The driver was run end to end against a live device, a WS-C3650-48PQ running IOS-XE 16.12.14.

INFO pyntc: Host [redacted]: File pyntc_ftp_test.bin transferred successfully with output: Accessing ftp://*:*@[redacted]/IOS-XE/pyntc_ftp_test.bin...!
[OK - 94038/4096 bytes]

94038 bytes copied in 0.159 secs (591434 bytes/sec)

PASSED: flash:pyntc_ftp_test.bin transferred and the md5 verified.

Fifteen new unit tests cover the IOS credential routing, the non-default port, the VRF token, the error detail and the loop guard. The error and loop-guard tests are mirrored on NX-OS, ASA and IOS-XR.

tests/integration/test_ios_device.py is new and skips unless its URL environment variables are set, so it runs against a lab device on demand and never in CI.

Follow-ups, not in this PR

• FileCopyModel.ftp_passive does nothing outside the Junos driver. IOS defaults to active FTP and would need ip ftp passive in global config.
• Six drivers repeat the same copy-command construction and prompt walk. The logic could be collapsed into a utils.py or base.py helper. That should likely be a separate PR, if desired.