Replace anonymous function usages on decode

[ypconstante]

This PR replaces anonymous function usages on decode to use recursion or named function references. This reduces a memory usage and reductions count, and brings a small performance improvement.

##### With input google_message1_proto2 #####
Name                                                            ips        average  deviation         median         99th %
decode (decode-replace-anonymous-func-e2aea63-decode)      425.90 K        2.35 μs  ±1737.36%        2.18 μs        3.92 μs
decode (main-1605e2b-decode)                               404.04 K        2.47 μs  ±1326.40%        2.31 μs        3.49 μs

Comparison: 
decode (decode-replace-anonymous-func-e2aea63-decode)      425.90 K
decode (main-1605e2b-decode)                               404.04 K - 1.05x slower +0.127 μs

Memory usage statistics:

Name                                                     Memory usage
decode (decode-replace-anonymous-func-e2aea63-decode)         4.02 KB
decode (main-1605e2b-decode)                                  4.38 KB - 1.09x memory usage +0.36 KB

**All measurements for memory usage were the same**

Reduction count statistics:

Name                                                  Reduction count
decode (decode-replace-anonymous-func-e2aea63-decode)             438
decode (main-1605e2b-decode)                                      470 - 1.07x reduction count +32

**All measurements for reduction count were the same**

##### With input google_message1_proto3 #####
Name                                                            ips        average  deviation         median         99th %
decode (decode-replace-anonymous-func-e2aea63-decode)      430.74 K        2.32 μs  ±1614.88%        2.16 μs        3.25 μs
decode (main-1605e2b-decode)                               407.90 K        2.45 μs  ±1117.13%        2.31 μs        3.49 μs

Comparison: 
decode (decode-replace-anonymous-func-e2aea63-decode)      430.74 K
decode (main-1605e2b-decode)                               407.90 K - 1.06x slower +0.130 μs

Memory usage statistics:

Name                                                     Memory usage
decode (decode-replace-anonymous-func-e2aea63-decode)         3.97 KB
decode (main-1605e2b-decode)                                  4.37 KB - 1.10x memory usage +0.40 KB

**All measurements for memory usage were the same**

Reduction count statistics:

Name                                                  Reduction count
decode (decode-replace-anonymous-func-e2aea63-decode)             422
decode (main-1605e2b-decode)                                      471 - 1.12x reduction count +49

**All measurements for reduction count were the same**

##### With input google_message2 #####
Name                                                            ips        average  deviation         median         99th %
decode (decode-replace-anonymous-func-e2aea63-decode)       10.83 K       92.30 μs     ±9.95%       91.34 μs      129.09 μs
decode (main-1605e2b-decode)                                10.80 K       92.60 μs    ±21.01%       91.69 μs      109.02 μs

Comparison: 
decode (decode-replace-anonymous-func-e2aea63-decode)       10.83 K
decode (main-1605e2b-decode)                                10.80 K - 1.00x slower +0.29 μs

Memory usage statistics:

Name                                                          average  deviation         median         99th %
decode (decode-replace-anonymous-func-e2aea63-decode)        96.41 KB     ±0.01%       96.41 KB       96.41 KB
decode (main-1605e2b-decode)                                 96.14 KB     ±0.00%       96.14 KB       96.14 KB

Comparison: 
decode (decode-replace-anonymous-func-e2aea63-decode)        96.41 KB
decode (main-1605e2b-decode)                                 96.14 KB - 1.00x memory usage -0.26556 KB

Reduction count statistics:

Name                                                  Reduction count
decode (decode-replace-anonymous-func-e2aea63-decode)         10.16 K
decode (main-1605e2b-decode)                                  10.19 K - 1.00x reduction count +0.0320 K

[whatyouhide]

I’m ok with this change but we should leave code comments explaining why we take this approach in these functions, otherwise the chance of someone going and eventually changing them back is a bit too high 🙃

[ypconstante]

Added a comment to update_in_message 0763f93