Retrieve info when using field references

Hi,

First of all, thanks for this great module.

I'm just wanna ask or report that when you have an entry where the user name and password are set as field reference, the value returned is not the actual value of the reference, but the field itself.
For instance, if I have a username set as {REF:U@T:MainAccount}, when I execute the following code I get:
```
$cred = Get-Secret -Vault KeePass -Name "MainAccount"
Write-Host $cred.GetNetworkCredential().Username
```
Result:
```
{REF:U@T:MainAccount}
```

However if the value of username of MainAccount is for instance jlanza, the result should have been jlanza and not the pointer to the value.

Thanks for you help.

Start by reproducing the Get-Secret call for a KeePass entry whose username uses the shown {REF:U@T:MainAccount} syntax, then trace how field references are handled during credential retrieval. Done means GetNetworkCredential().Username returns the referenced value, such as jlanza, rather than the reference string.

Written by the indexing model from the issue text.