[Target] Keep all implied features in canonical representation

[alexreinking]

Following up on my comment in #9241.

This adjusts Target to always have a single, stable, representation by filling in implied target features.

This leans into the mathematical lattice structure targets have.

Breaking changes

The target.to_string() function now shows a minimal target; clients wanting to see everything should use .to_complete_target().

Checklist

• Tests added or updated (not required for docs, CI config, or typo fixes)
• Documentation updated (if public API changed)
• Python bindings updated (if public API changed)
• Benchmarks are included here if the change is intended to affect performance.
• Commits include AI attribution where applicable (see Code of Conduct)

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[codecov]

Codecov Report

❌ Patch coverage is 65.31792% with 60 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.29%. Comparing base (efa1918) to head (d2d71c7).

Files with missing lines	Patch %	Lines
src/Target.cpp	65.24%	39 Missing and 18 partials ⚠️
src/CodeGen_X86.cpp	0.00%	1 Missing and 1 partial ⚠️
src/StmtToHTML.cpp	50.00%	1 Missing ⚠️

Additional details and impacted files

@@                      Coverage Diff                       @@
##           alexreinking/target-tables    #9253      +/-   ##
==============================================================
- Coverage                       70.30%   70.29%   -0.01%     
==============================================================
  Files                             255      255              
  Lines                           78819    78757      -62     
  Branches                        18879    18843      -36     
==============================================================
- Hits                            55412    55366      -46     
- Misses                          17809    17849      +40     
+ Partials                         5598     5542      -56     

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