Made the compatibility check also include bincode 2 serde, and added comments

[VictorKoenders]

Some of the code was redundant because we confirmed that the bincode_1_output was identical to the bincode_2_output. Therefor deserializing the same slice twice won't give different results.

Added a validation that bincode_2::serde also (de)serializes the same.

[codecov]

Codecov Report

Merging #501 (dc1efac) into trunk (8c0b68b) will increase coverage by 0.72%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##            trunk     #501      +/-   ##
==========================================
+ Coverage   68.35%   69.07%   +0.72%     
==========================================
  Files          43       43              
  Lines        3049     3056       +7     
==========================================
+ Hits         2084     2111      +27     
+ Misses        965      945      -20     

Impacted Files	Coverage Δ
compatibility/src/lib.rs	50.90% <85.71%> (ø)
src/features/serde/ser.rs	33.96% <0.00%> (+9.92%)	⬆️
src/features/serde/de_owned.rs	42.45% <0.00%> (+13.73%)	⬆️

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