Add parse validation helpers, tests, and docs updates

[Jim8y]

Summary

• add parse helper and runtime parsing for UInt160/UInt256/ECPoint with validation
• update compiler/analyzer/tests to use Parse for constants and runtime parsing fallbacks
• refresh security docs with Parse-based examples and new parse unit tests

Testing

• dotnet test tests/Neo.SmartContract.Framework.UnitTests/Neo.SmartContract.Framework.UnitTests.csproj -c Release
• dotnet test tests/Neo.SmartContract.Analyzer.UnitTests/Neo.SmartContract.Analyzer.UnitTests.csproj -c Release
• dotnet test neo-devpack-dotnet.sln -c Release (started; main suites pass; compiler unit tests may need rerun if desired)

[shargon]

Is not full covered now?

[shargon]

I think we only use full read, or I miss something? It will be clear a regular ParseHex(byte[] data)

[Wi1l-B0t]

Suggested change

	throw new FormatException("Invalid hex character.");
	throw new FormatException("Invalid hex character: ${value}.");

[Wi1l-B0t]

Suggested change

	internal static byte[] ParseHex(byte[] valueBytes, int offset, int expectedLength)
	{
	int hexLength = valueBytes.Length - offset;
	if (hexLength != expectedLength * 2)
	throw new FormatException("Invalid hex length.");
	byte[] result = new byte[expectedLength];
	for (int i = 0; i < expectedLength; i++)
	{
	byte high = FromHexByte(valueBytes[offset + i * 2]);
	byte low = FromHexByte(valueBytes[offset + i * 2 + 1]);
	result[i] = (byte)((high << 4) | low);
	}
	return result;
	}
	internal static byte[] ParseHex(byte[] valueBytes, int offset, int expectedLength)
	{
	int hexLength = valueBytes.Length - offset;
	if (hexLength != expectedLength * 2)
	throw new FormatException("Invalid hex length.");
	return Convert.FromHexString(valueBytes.AsSpan()[offset..]);
	}

This is better?