Added the possibility to memoize proxies in an optimistic way

[WebReflection]

This variant adds little code, not much extra logic when timeout option is not used, but it can drastically reduce the amount of roundtrips needed to retrieve (especially repeatedly) same values per proxy, improving performance specially when libraries that access all the time same properties are part of the worker/remote logic.

To be considered

• the approach is optimistic: there is no guarantee that if a value is cached is reflected with the same value elsewhere
• mostly keys and get traps benefit from it, all other traps must invalidate memoized keys (delete, defineProperty, etc)
• the logic is slower on both local and remote for get trap because it cannot cache properties with accessors but the outcome is less roundtrip, serialization and whatnot ... it might be a win-win or useless, time will tell
• timeout option is used to schedule a cleanup of all cached keys and related values per each proxy. If -1 (default) there won't be any cache used at all, if 0 (suggested) or greater, it dictates for how long properties should be cached.

Please note that the cache is a forever growing list of proxies and keys to drop so that passing Infinity, as example, is a very bad idea, but in general the logic should just work nicely within the current "tick" and all drops and sync delayed after.

Performance when no timeout is used should not be affected much, it's just an if condition with no extra or different logic attached (from the previous version).

[coveralls]

Pull Request Test Coverage Report for Build 15873749662

Details

• 121 of 121 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.05%) to 99.951%

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Totals
Change from base Build 15774551367:	-0.05%
Covered Lines:	1651
Relevant Lines:	1651

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💛 - Coveralls