wip(syrup): syrup reader, writer, and codecs for efficient parsing

[kumavis]

replaced by #2766

wip improvement to syrup -- working towards allowing a future consumer (eg OCapN) to lazily parse syrup messages without reifying all encountered values

see test file https://github.com/endojs/endo/blob/7632803791dc6160c39c1af33963f52e0f2730ec/packages/syrup/test/parse.test.js

[kriskowal]

This unfortunately registers every symbol encountered in a global table that isn’t necessarily garbage collected.

My intuition is that we’ll need to either wrap every value in a wrapper object like {type: 'symbol', symbol: 'hello'} or just wrap all non-primitive values, including list, struct, and record, like {type: 'record', record: [1, 2, 3]} and {type: 'list', list: [1, 2, 3]}.

[kriskowal]

This is also why we’re now calling Syrup symbols “Selector”. They do not necessarily correspond to implementation-language symbols.

[kumavis]

i made them prefixed symbols so that they can be keys on dictionaries (represented as js objects) though I don't create them when they are Record labels, as used in ocapn messages.

could create a custom clearable symbol registry though Symbol('hi') !== Symbol.for('hi')

as well as other options

[kumavis]

separate branch with symbol -> selector rename https://github.com/endojs/endo/compare/kumavis-syrup-lazy-parse...kumavis-syrup-lazy-parse-selector?expand=1

update: merged here

[kumavis]

replaced by #2766