Introduce StructuredRunOpt for more complex runopts

[AbishekS]

Summary:
StructuredRunOpt can be used to create new complex runopts

This can be used as for example:

    dataclass
    class UlimitTest(StructuredRunOpt):
        name: str
        hard: int
        soft: int

        def template(self) -> str:
            return "{name},{soft:d},{hard:d}"

This comes with

1. template() that helps the from_repr() use that template to map to the fields with types
2. eq to check equality between two

Differential Revision: D85159071

[meta-codesync]

@AbishekS has exported this pull request. If you are a Meta employee, you can view the originating Diff in D85159071.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.35294% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.54%. Comparing base (5053c87) to head (2bf5da2).

Files with missing lines	Patch %	Lines
torchx/specs/api.py	82.35%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1154      +/-   ##
==========================================
- Coverage   91.56%   91.54%   -0.03%     
==========================================
  Files          83       83              
  Lines        6593     6610      +17     
==========================================
+ Hits         6037     6051      +14     
- Misses        556      559       +3     

Flag	Coverage Δ
unittests	91.54% <82.35%> (-0.03%)	⬇️

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