Fix Error Message

[willtebbutt]

The rather cryptic error message shown in #310 is the result of a bug. This PR improves this error message by giving it is own type, and tests that it throws correctly when expected to do so.

[codecov]

Codecov Report

Attention: Patch coverage is 38.46154% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/interpreter/s2s_reverse_mode_ad.jl	38.46%	16 Missing ⚠️

Files with missing lines	Coverage Δ
src/interpreter/s2s_reverse_mode_ad.jl	92.55% <38.46%> (-0.10%)	⬇️

[github-actions]

Performance Ratio:
Ratio of time to compute gradient and time to compute function.
Warning: results are very approximate! See here for more context.

┌────────────────────────────┬──────────┬──────────┬─────────────┬─────────┐
│                      Label │ Mooncake │   Zygote │ ReverseDiff │  Enzyme │
│                     String │   String │   String │      String │  String │
├────────────────────────────┼──────────┼──────────┼─────────────┼─────────┤
│                   sum_1000 │     68.6 │      1.0 │        5.41 │ missing │
│                  _sum_1000 │     6.67 │ 335000.0 │        34.6 │ missing │
│               sum_sin_1000 │     2.22 │     1.68 │        10.5 │ missing │
│              _sum_sin_1000 │     2.56 │    237.0 │        12.9 │ missing │
│                   kron_sum │     83.1 │     5.04 │       274.0 │ missing │
│              kron_view_sum │     65.5 │     10.3 │       270.0 │ missing │
│      naive_map_sin_cos_exp │     2.53 │  missing │        7.11 │ missing │
│            map_sin_cos_exp │     2.77 │     1.42 │        6.33 │ missing │
│      broadcast_sin_cos_exp │     2.66 │     2.25 │        1.45 │ missing │
│                 simple_mlp │      7.7 │     4.33 │        16.9 │ missing │
│                     gp_lml │     4.54 │     1.55 │     missing │ missing │
│ turing_broadcast_benchmark │     3.79 │  missing │        22.9 │ missing │
│         large_single_block │     4.03 │   3990.0 │        30.2 │ missing │
└────────────────────────────┴──────────┴──────────┴─────────────┴─────────┘