invoke attempt 2

[willtebbutt]

This PR largely resolves #206 -- in particular it makes invoke(f, TT, args...) work nicely when f and TT can be resolved statically.

[github-actions]

Performance Ratio:
Warning: results are very approximate!

┌────────────────────────────┬────────┬─────────┬─────────────┬─────────┐
│                      Label │  Tapir │  Zygote │ ReverseDiff │  Enzyme │
│                     String │ String │  String │      String │  String │
├────────────────────────────┼────────┼─────────┼─────────────┼─────────┤
│                        sum │   30.4 │   0.324 │        2.26 │   0.632 │
│                       _sum │   6.71 │   516.0 │        27.2 │   0.121 │
│                   kron_sum │   76.9 │    3.51 │       210.0 │    25.8 │
│              kron_view_sum │   91.0 │    10.8 │       254.0 │    8.71 │
│      naive_map_sin_cos_exp │   4.06 │ missing │        8.62 │    2.78 │
│            map_sin_cos_exp │   4.91 │    1.81 │        7.52 │    3.42 │
│      broadcast_sin_cos_exp │   4.41 │    2.64 │        1.66 │    2.82 │
│                 simple_mlp │    8.9 │    3.11 │        14.8 │    3.17 │
│                     gp_lml │   15.6 │     4.5 │     missing │ missing │
│ turing_broadcast_benchmark │   9.09 │ missing │        28.0 │ missing │
└────────────────────────────┴────────┴─────────┴─────────────┴─────────┘