Fix some ChainRulesCore invalidations

[timholy]

ChainRulesCore gets loaded by a lot of packages. Its fallback methods

==(a, b::AbstractThunk)
==(a::AbstractThunk, b)

invalidate a lot of things, including much of the Serialization stdlib. But at least we can protect JuliaInterpreter.

[timholy]

Before:

 inserting ==(a::AbstractThunk, b) in ChainRulesCore at /home/tim/.julia/packages/ChainRulesCore/IzITE/src/tangent_types/thunks.jl:28 invalidated:
   backedges: 1: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::Task) (4 children)
              2: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::JuliaInterpreter.SlotNumber) (7 children)
              3: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::Base.UUID) (9 children)
              4: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::FileWatching._FDWatcher) (22 children)
              5: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::Symbol) (280 children)

After:

 inserting ==(a::AbstractThunk, b) in ChainRulesCore at /home/tim/.julia/packages/ChainRulesCore/IzITE/src/tangent_types/thunks.jl:28 invalidated:
   backedges: 1: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::Task) (4 children)
              2: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::Base.UUID) (9 children)
              3: superseding ==(x, y) in Base at Base.jl:119 with MethodInstance for ==(::Any, ::FileWatching._FDWatcher) (22 children)

[codecov]

Codecov Report

Merging #530 (f19c224) into master (79e3d2b) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #530      +/-   ##
==========================================
+ Coverage   87.40%   87.41%   +0.01%     
==========================================
  Files          12       12              
  Lines        2470     2472       +2     
==========================================
+ Hits         2159     2161       +2     
  Misses        311      311              

Impacted Files	Coverage Δ
src/commands.jl	93.45% <100.00%> (ø)
src/utils.jl	88.28% <100.00%> (+0.05%)	⬆️

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