Add -Encoding parameter to MemoryStream string functions (#21)

[austoonz]

Summary

Adds the -Encoding parameter to ConvertFrom-MemoryStreamToString and ConvertFrom-MemoryStreamToSecureString functions, resolving the inconsistency where these functions hardcoded UTF-8 encoding while other similar functions in the module support encoding selection.

Changes

New Features

• Added -Encoding parameter to ConvertFrom-MemoryStreamToString
• Added -Encoding parameter to ConvertFrom-MemoryStreamToSecureString
• Both default to UTF8 for backward compatibility
• Supported encodings: ASCII, BigEndianUnicode, Default, Unicode, UTF32, UTF8

Fixed

• ConvertFrom-MemoryStream now correctly passes -Encoding to ConvertFrom-MemoryStreamToString for consistent behavior across the module

Tests

• Added encoding tests for both functions covering all supported encodings
• Updated ConvertFrom-MemoryStream tests to create streams with correct encoding

Documentation

• Updated function documentation with new parameter
• Updated CHANGELOG

Example

# Create a MemoryStream with UTF-16 encoded content
$bytes = [System.Text.Encoding]::Unicode.GetBytes("Hello World")
$stream = [System.IO.MemoryStream]::new($bytes)

# Now works correctly with -Encoding parameter
$stream | ConvertFrom-MemoryStreamToString -Encoding Unicode
# Output: "Hello World"

Closes #21