Encapsulated encoders

[wlandau]

Prework

• Read and abide by drake's code of conduct.
• Search for duplicates among the existing issues, both open and closed.

Description

We have 4 hash tables to encode and decode paths and namespaced functions.

• ht_encode_path
• ht_decode_path
• ht_encode_namespaced
• ht_decode_namespaced

Let's add some OOP. We could create a new "encoder" class that inherits from the hash table class. Depends on #967.

[wlandau]

Let's use object composition instead of inheritance.

[wlandau]

Idea:

• Create an encoder class to encode and decode stuff.
• Create an encoder_path with ht_encode_path and ht_decode_path().
• Create another for namespaces.
• Maybe also deal with progress_hashmap this way too.
• Group these in an encoders field of config.

[wlandau]

Nope, let's just make encoding and decoding part of the decorated storr.

[wlandau]

Yup, extra functions in the decorated storr capture all of this. It completes the encapsulation, moving from exposed hash tables to reference class methods that use them under the hood.

[wlandau]

Just need to verify that #1011 did not reduce performance.

[wlandau]

Just ran a couple versions of the overhead example. Flame graphs look the same as before with no obvious bottlenecks.