Fix IEx.Helpers.r/1 fails reload modules defined in same file

[AlexGx]

Two modules defined in one file:

defmodule Foo do
    def hello, do: :foo
end

defmodule Bar do
    def hello, do: :bar
end

Trying to reload after compilation:

iex> r([Bar, Foo])

    ...
    
    error: cannot define module Foo because it is currently being defined in /tmp/reload.ex:1
    │
  1 │ defmodule Foo do
    │ ^^^^^^^^^^^^^^^^
    │
    └─ /tmp/reload.ex:1: Foo (module)


= Compilation error in file /tmp/reload.ex ==
** (CompileError) /tmp/reload.ex: cannot compile module Foo (errors have been logged)
    (stdlib 8.0.2) lists.erl:2465: :lists.foldl/3
    (elixir 1.21.0-dev) lib/kernel/parallel_compiler.ex:549: anonymous fn/5 in Kernel.ParallelCompiler.spawn_workers/8
** (MatchError) no match of right hand side value:

Expected: {:reloaded, [Bar, Foo]}

Changes:

• add elixir sources dedup
• tests

[josevalim]

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