Add AsOneString parameter to ConvertTo-Base64 for single string encoding

[Copilot]

Changes

This PR adds a new -AsOneString switch parameter to the ConvertTo-Base64 function that allows users to encode multiple input lines as a single base64 string, similar to how the Linux base64 utility works.

Before:

Get-Content -Path file.txt | ConvertTo-Base64
# Results in multiple base64 strings (one per line in the file)
TGluZSAx
TGluZSAy
TGluZSAz

After:

Get-Content -Path file.txt | ConvertTo-Base64 -AsOneString
# Results in a single base64 string with all lines joined by newlines
TGluZSAxCkxpbmUgMgpMaW5lIDM=

Implementation Details

• Added -AsOneString switch parameter to allow joining inputs with newlines
• Used begin/process/end blocks to accumulate input when the switch is used
• Updated documentation with new examples showing the parameter usage
• Added tests to verify the functionality

Example using a file:

$content = Get-Content -Path test.txt
# Without -AsOneString (each line encoded separately):
$content | ConvertTo-Base64
# With -AsOneString (all joined with newlines and encoded as one):
$content | ConvertTo-Base64 -AsOneString

This matches the behavior requested in the issue where the user wanted to encode file content as a single base64 string, similar to the Linux base64 utility.

Fixes #7.

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