Using a data probing strategy, efficiently retrieve the top level tag to determine which top level parser to use

[DJBen]

• This change makes all the parsing errors in partwise documents MUCH more understandable because it will no longer be swallowed.
• This change also increases parsing speed for timewise documents because it will no longer attempt to parse it with partwise parser first.

[codecov-io]

Codecov Report

Merging #202 into latest will increase coverage by 0.12%. The diff coverage is 94.82%.

@@            Coverage Diff             @@
##           latest     #202      +/-   ##
==========================================
+ Coverage   72.03%   72.16%   +0.12%     
==========================================
  Files         218      218              
  Lines        3662     3715      +53     
==========================================
+ Hits         2638     2681      +43     
- Misses       1024     1034      +10

Impacted Files	Coverage Δ
Sources/MusicXML/Complex Types/Score.swift	66.66% <100%> (+20.51%)	:arrow_up:
Sources/MusicXML/Decoding/Decoding.swift	92.45% <93.47%> (+4.95%)	:arrow_up:
...ces/MusicXML/Complex Types/Timewise/Timewise.swift	74.07% <0%> (-25.93%)	:arrow_down:

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[bwetherfield]

Thank you so much for contributing this, @DJBen! Looks amazing. Just the one question I had regarding the use of XMLDecoder.userInfo versus storing the relevant Score.CodingKeys value directly.

[jsbean]

This looks great to me!