[WIP] Improve parse error

[seanmcl]

Attempts to address #19 Currently reports the column of the closing quote of the operator. Not amazing, but also not clear how to get the starting column. Perhaps it's embedded in the hd of state.trace but I haven't grokked the parser enough yet to know.

Definitely open to feedback on this one!

Example:

"builtin.module"() ({
  "func.func"() <{function_type = (tensor<28x28xf32>, tensor<784x10xf32>, tensor<1x10xf32>) -> tensor<1x10xf32>, sym_name = "main"}> ({
  ^bb0(%arg0: tensor<28x28xf32>, %arg1: tensor<784x10xf32>, %arg2: tensor<1x10xf32>):
    %0 = "stablehlo.reshape"(%arg0) : (tensor<28x28xf32>) -> tensor<1x784xf32>
    %1 = "stablehlo.dot"(%0, %arg1) : (tensor<1x784xf32>, tensor<784x10xf32>) -> tensor<1x10xf32>
    %2 = "stablehlo.add"(%1, %arg2) : (tensor<1x10xf32>, tensor<1x10xf32>) -> tensor<1x10xf32>
    %3 = "stablehlo.constant"() <{value = dense<0.000000e+00> : tensor<1x10xf32>}> : () -> tensor<1x10xf32>
    %4 = "stablehlo.foo"(%2, %3) : (tensor<1x10xf32>, tensor<1x10xf32>) -> tensor<1x10xf32>
    "func.return"(%4) : (tensor<1x10xf32>) -> ()
  }) : () -> ()
}) : () -> ()

Parsing error line 8, column 23 : Unknown op code: 'foo'