fix: pcap file name formatting

[kamilprz]

Description

Fix the bad formatting of the pcap file names when running retina capture create.

Also adding testing for the utilities around how file names are created.

Related Issue

#1732

Checklist

• I have read the contributing documentation.
• I signed and signed-off the commits (git commit -S -s ...). See this documentation on signing commits.
• I have correctly attributed the author(s) of the code.
• I have tested the changes locally.
• I have followed the project's style guidelines.
• I have updated the documentation, if necessary.
• I have added tests, if applicable.

Screenshots (if applicable) or Testing Completed

The below shows a successful download of a packet capture which is then extracted. The final grep shows the file name of the .pcap which is in the same format as the .tar.gz.

~/src/retina git:kamilp/capture-filename-format
> k retina capture download --name pcap-filename -o ./downloads

File to be downloaded:  /host/mnt/retina/captures/pcap-filename-aks-agentpool-33289083-vmss000000-20250716220911UTC.tar.gz
Creating download pod: pcap-filename-download-d49wc
Obtaining file...
Bytes retrieved: 189453
File written to:  downloads/pcap-filename/pcap-filename-aks-agentpool-33289083-vmss000000-20250716220911UTC.tar.gz

File to be downloaded:  /host/mnt/retina/captures/pcap-filename-aks-agentpool-33289083-vmss000001-20250716220911UTC.tar.gz
Creating download pod: pcap-filename-download-t86dl
Obtaining file...
Bytes retrieved: 277310
File written to:  downloads/pcap-filename/pcap-filename-aks-agentpool-33289083-vmss000001-20250716220911UTC.tar.gz
                                                                                                                               ~/src/retina git:kamilp/capture-filename-format*
> cd ./downloads/

~/src/retina/downloads git:kamilp/capture-filename-format*
> mkdir extract

~/src/retina/downloads git:kamilp/capture-filename-format*
> tar -xvf pcap-filename/pcap-filename-aks-agentpool-33289083-vmss000001-20250716220911UTC.tar.gz -C extract/

~/src/retina/downloads git:kamilp/capture-filename-format*
> cd extract/                                                                                                                    

~/src/retina/downloads/extract git:kamilp/capture-filename-format*
> ll | grep ".pcap"
.rw-r--r-- kamilp 557 KB 2025-07-16 23:09:23 pcap-filename-aks-agentpool-33289083-vmss000001-20250716220911UTC.pcap

[SRodi]

LGTM