OPEN-79: Support for zeroizing Asn1Encoder/WriterScope via VecOfU8

[simon-void]

support for zeroizing datatype VecOfU8.
Please check during review if throughout the code the appropriate variant of VecOfU8 is used!
Zeroizing is more secure but takes additional time (because its memory will be overriden by 0s on Drop).
NonZeroizing is less secure but faster.

Changes

• introduces a new VecOfU8 enum with two variants Zeroizing and NonZeroizing which is used in many places instead of a Vec
• if VecOfU8::Zeroizing is used it's underlying Vec is zeroed on drop
• the Asn1Encoder now contains two write-functions (instead of one retrning a Vec), one returning a VecOfU8::Zeroizing and one returning a VecOfU8::NonZeroizing

Breaking Changes

• None

Checklist

• Tests added/updated where appropriate
• FFI targets (swift, kotlin, ...) are updated where appropriate
• Public API is documented
• Docs updated (docs/, README.md) if needed
• Release notes updated (ReleaseNotes.md) if user-facing change

[tobias-schwerdtfeger]

Needs to be the same type of VecOfU8 somehow