Move calc_id into job.py

[vyasr]

Description

Move hashing.calc_id into the job module. The parameter is also renamed from spec to statepoint to more accurately reflect its usage.

Motivation and Context

The id computed by hashing.calc_id is not a generic hash id. It is very specifically tied to the project-job-statepoint relationship that forms the core data model in signac. This move helps clarify that. Additionally, if we ever move to support more general file layouts, this move ensures that the calculated id is tightly coupled to the Job class.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[codecov]

Codecov Report

Merging #873 (9b4fca0) into master (3de5f48) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #873      +/-   ##
==========================================
- Coverage   86.53%   86.52%   -0.02%     
==========================================
  Files          41       40       -1     
  Lines        4531     4527       -4     
  Branches      901      901              
==========================================
- Hits         3921     3917       -4     
  Misses        429      429              
  Partials      181      181              

Impacted Files	Coverage Δ
signac/job.py	89.93% <100.00%> (+0.19%)	⬆️
signac/project.py	89.96% <100.00%> (-0.02%)	⬇️

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[bdice]

I kind of liked the shared hashing functionality being in its own module, but I don't feel strongly. I accept this.