remove `shallow` usages for ORC

[ringabout]

shallow doesn't work for ARC/ORC.

proc shallow*[T](s: var seq[T]) {.noSideEffect, inline.} =
  ## Marks a sequence `s` as `shallow`:idx:. Subsequent assignments will not
  ## perform deep copies of `s`.
  ##
  ## This is only useful for optimization purposes.
  if s.len == 0: return
  when not defined(js) and not defined(nimscript) and not defined(nimSeqsV2):
    var s = cast[PGenericSeq](s)
    s.reserved = s.reserved or seqShallowFlag

Should we remove it from system for ARC/ORC? or deprecated it since it can only be used for optimizations.

[arnetheduck]

or deprecated it since it can only be used for optimizations.

it's not only optimizations - it significantly changes semantics because the shallow operation enables shared mutable instances (which semantically is problematic in general) which in turn changes the meaning of programs using it, beyond optimisation (it's observable) - removing completely for orc seems reasonable.

[ringabout]

it's not only optimizations - it significantly changes semantics because the shallow operation enables shared mutable instances (which semantically is problematic in general) which in turn changes the meaning of programs using it, beyond optimisation (it's observable)

True, but it is documented at least => "This is only useful for optimization purposes."

removing completely for orc seems reasonable.

I will go for it, though I cannot manage to fix every important package by myself very soon. shallowCopy has broken lots of packages in my PR(defaults to ORC).

[arnetheduck]

True, but it is documented at least

documentation is wrong - perhaps whoever wrote it didn't consider the semantic consequences, but they are there nonetheless, and likely relied upon in edge-case code which makes it harder to detect - better remove and make it break visibly.

shallowCopy has broken lots of packages in my PR(defaults to ORC).

this is the easy part of moving to orc ;) at least it breaks visibly.

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