WIP: Lwt-result-stdlib meta-MR

Meta-MR:

• Bigger Lwtreslib

  • !1903 (merged)
  • !1904 (merged)
  • !1905 (merged)
  • !1968 (merged)
  • !1895 (merged)
  • !2050 (merged)
  • !1967 (closed) and !2245 (merged) (List( with Tests), depends on !2244 (merged) and !2243 (merged))
  • !2054 (merged) (Option, Result)
  • Arrays (Maybe not appropriate?)
  • String?
  • !2642 (merged) Seq_s (Lwt-aware seqs), Seq_e (error-aware seqs), etc.
  • !2761 (closed) iter_n: like iter_p but with a limit on concurrency (see Lwt_list), or just ?max_concurrency for all _p
  • !2886 (merged) helpers for exception-error conversion (catch/raise)

• Better Lwtreslib

  • !2018 (merged)
  • !2244 (merged) (Tests for Seq and Set)
  • !2054 (merged) Unsafe module for convenience (e.g., Unsafe.Option.find ~__LOC__ o; e.g., Unsafe.Result.get_ok ~__LOC__)
  • !2642 (merged) Require explicit ~comparison argument instead of relying on polymorphic comparison (e.g., List.mem, List.assoc).
  • Æsthetically uniform code (e.g., Lwt.return_ok vs Monad.return vs Lwt.return (Ok ))
  • !2026 (merged) (More independence from Error-monad, rearrange Seq.Monad at the same time)
  • #1425 (closed) tiered monad? tiered syntax? lets?

• Misc

  • !2036 (merged)
  • !2243 (merged)
  • !2994 (merged) (Option.filter, counterpart to List.filter)

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This meta-MR introduces tezos-lwt-result-stdlib, a library with Set, Map and other collections that are similar to Stdlib's but

• without any exceptions and
• with support for error, lwt, and combined error-lwt monad traversal.

The ultimate aim is to shadow the Stdlib's version to enforce use of the error monad.

future steps

• Add support Lwtreslib in the protocol environment
• Increase shadowing of the Stdlib:
  • Option
  • Array
  • Seqlwt (a Seq-like module that has more integration with Lwt, this should allow to have a lazy map) (Wouldn't Lwt_stream suffice?)
  • Queue
• make the trace abstract/private (to prevent #864 from ever happening) with generic enough combinators (seuqntial for tracing, concurrent for combining)
• Absorb TzString and TzList extensions possibly?