[N4] unwrap StorageKey

[shargon]

Description

Required for #4348

This pull request introduces a new parsing capability to the KeyBuilder class in the smart contract library, allowing for extraction of key components from a byte array, and adds corresponding unit tests to verify this functionality. The most important changes are grouped below by theme.

KeyBuilder enhancements

• Added a new internal static method TryParse to KeyBuilder that parses a byte array into its constituent id, prefix, and value fields, supporting multiple value types. This improves the ability to decompose storage keys for inspection or validation.
• Implemented a helper method ReadStruct for safely reading value types from a byte span using marshaling.
• Removed the unused constant PrefixLength from KeyBuilder, simplifying the class.

Unit testing

• Added a new test method TestTryParse to UT_KeyBuilder.cs to verify correct parsing of various key formats and error conditions for the new TryParse method.
• Updated test imports to include System.Reflection, supporting new test logic.

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Unit Testing
• Run Application
• Local Computer Tests
• No Testing

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[shargon]

@erikzhang we loose performance here, because in regular nodes we always need to reverse each key, before the change this was faster

[erikzhang]

Have you tested it? Approximately how much performance was lost?

[shargon]

I don't have a benchmark. it depends a lot on the key size, but previously an integer was written directly inverted, and now it requires an extra loop to reverse it. Also, I think a string gets reversed, and it shouldn't; only an integer should be reversed.

[erikzhang]

string is not a value type.

[erikzhang]

If it is used for #4348, I think it's easy to extract Offset from the Value.