[WIP] Developing alphabetical identifier for future MPID use

[esoteric-ephemera]

Defines a new AlphaID class that could eventually replace / contain the current MPID class.

From internal discussions, the benefit of the MPID system was brevity when the system was relatively new. "mp-149" is easy to remember whereas the current batch of MPIDs are > 3,000,000.

To replace / augment the current MPID system, we need an identifier that:

• Can be sorted
• Can mint an $N+1$ ID given that $N$ IDs have currently been assigned
• Is easy to remember

From this, it was suggested that an alphabetical string (to avoid clashes with the current MPIDs, no numbers can be used) could be used instead. The integer value of this string would essentially be taken as base-26 representation, i.e.:

• "a" = $0 \times 26^0 = 0$
• "bc" = $1 \times 26^1 + 2 \times 26^0 = 28$
• "aaft" = $0 \times 26^3 + 0 \times 26^2 + 5 \times 26^1 + 19 \times 26^0 = 149$

The current implementation supports these features, as well as addition/subtraction to obtain the sequentially next identifier, used when parsing. To make these easy to remember, we may want to set the pad length (the number of leading zeroes or "a" characters) to be at least 6, which would give us $26^6 = 308,915,776$ total task IDs (minus the ~3,100,000 that have currently been assigned).

Suggestions / discussion are welcome

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.11765% with 4 lines in your changes missing coverage. Please review.

Project coverage is 90.20%. Comparing base (200c970) to head (638453f).

Files with missing lines	Patch %	Lines
emmet-core/emmet/core/mpid.py	94.11%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1178      +/-   ##
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+ Coverage   90.18%   90.20%   +0.01%     
==========================================
  Files         147      147              
  Lines       14503    14570      +67     
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+ Hits        13080    13143      +63     
- Misses       1423     1427       +4     

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