Implement more powerful tree-join, fix tests on Julia-1.8

[timholy]

Julia-1.8 reports invalidations slightly differently from previous
versions. This harmonizes the output and avoids duplicating
trees/roots/branches.

While this suffices to fix SnoopCompile on 1.8, nightly will require additional work (failure anticipated).

[codecov]

Codecov Report

Base: 80.24% // Head: 86.03% // Increases project coverage by +5.78% 🎉

Coverage data is based on head (365f218) compared to base (ccbafd6).
Patch coverage: 72.50% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #292      +/-   ##
==========================================
+ Coverage   80.24%   86.03%   +5.78%     
==========================================
  Files          17       17              
  Lines        1929     2098     +169     
==========================================
+ Hits         1548     1805     +257     
+ Misses        381      293      -88     

Impacted Files	Coverage Δ
src/invalidations.jl	86.71% <72.50%> (+9.53%)	⬆️
SnoopCompileCore/src/snoopi_deep.jl	92.00% <0.00%> (-3.66%)	⬇️
SnoopPrecompile/src/SnoopPrecompile.jl	81.25% <0.00%> (-0.90%)	⬇️
src/parcel_snoopc.jl	78.15% <0.00%> (-0.23%)	⬇️
src/visualizations.jl	0.00% <0.00%> (ø)
src/parcel_snoopi.jl	94.14% <0.00%> (+0.30%)	⬆️
src/parcel_snoopl.jl	90.00% <0.00%> (+0.52%)	⬆️
src/write.jl	92.30% <0.00%> (+1.00%)	⬆️
src/deep_demos.jl	58.97% <0.00%> (+1.07%)	⬆️
src/parcel_snoopi_deep.jl	89.98% <0.00%> (+3.23%)	⬆️
... and 2 more

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