Using state variable comparison in annotations with `mstore` mode

Here is a small example:
```solidity
contract Sample {
uint public a;

/// #try a == 1;
function foo(uint256 x, uint256 y, uint256 z) pure public returns (uint256) {
return x + y + z;
}
}
```
With current Scribble version (0.6.22) it produces following output:
```bash
scribble ./sample.sol --instrumentation-metadata-file ./test.json --user-assert-mode mstore
```
```solidity
/// This file is auto-generated by Scribble and shouldn't be edited directly.
/// Use --disarm prior to make any changes.
pragma solidity 0.8.19;

contract Sample {
struct vars0 {
uint256 __mstore_scratch__;
}

uint public a;

function foo(uint256 x, uint256 y, uint256 z) public pure returns (uint256 RET_0) {
vars0 memory _v;
unchecked {
if (a == 1) _v.__mstore_scratch__ = 42;
}
RET_0 = _original_Sample_foo(x, y, z);
}

function _original_Sample_foo(uint256 x, uint256 y, uint256 z) private pure returns (uint256) {
return (x + y) + z;
}
}
```
Output is not compiled due to `foo()` is declared as `pure`, but it should be `view` as it now contains state variable check:
```solidity
if (a == 1) _v.__mstore_scratch__ = 42;
```
Diggig code for finding a root cause led me to following:
https://github.com/ConsenSys/scribble/blob/d397fc877baf3490c9a60d1e2b0bea7793fb96d7/src/instrumenter/instrument.ts#L99-L103
Then in `interpose()` we have
https://github.com/ConsenSys/scribble/blob/d397fc877baf3490c9a60d1e2b0bea7793fb96d7/src/instrumenter/interpose.ts#L212-L216
and basic assumption of following somehwere there also
https://github.com/ConsenSys/scribble/blob/d397fc877baf3490c9a60d1e2b0bea7793fb96d7/src/instrumenter/interpose.ts#L370-L384

Seems that we still have edge-cases when annotations can cause state muntability elevation from `pure` to `view` or non-payable due to instrumentation. Unless I miss something. If so, we should at least throw an error so user would get idea that something is wrong with the annotation.

Regards.