Check size is not greater than 8 for RV32A and RV63A

[mininny]

Description

The RV63A and RV32A operations are supported by the VM implementations.
The corresponding instructions encode the size in the funct3 field.

The Solidity implementation ensures that the size is correct by checking that it is not lower than 4 and not greater than 8.

        // 0b010 == RV32A W variants
        // 0b011 == RV64A D variants
        let size := shl64(funct3, toU64(1))
        if or(lt64(size, toU64(4)), gt64(size, toU64(8))) { revertWithCode(0xbada70) } // bad AMO size

However, the Go slow and fast implementations only check that the size is not lower than 4.
There is no check to ensure it is not greater than 8.

	// 0b010 == RV32A W variants
	// 0b011 == RV64A D variants
	size := shl64(funct3, toU64(1))
	if lt64(size, toU64(4)) != 0 {
		revertWithCode(riscv.ErrBadAMOSize, fmt.Errorf("bad AMO size: %d", size))
	}

The Go implementations (slow and fast) should ensure that the size is not greater than 8.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.89%. Comparing base (8ff9318) to head (36b7895).

Files with missing lines	Patch %	Lines
rvgo/fast/vm.go	0.00%	0 Missing and 1 partial ⚠️
rvgo/slow/vm.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #103   +/-   ##
=======================================
  Coverage   61.89%   61.89%           
=======================================
  Files          27       27           
  Lines        4091     4091           
=======================================
  Hits         2532     2532           
  Misses       1427     1427           
  Partials      132      132           

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