add smooth clamping operator

[nmbader]

JopClampC1: smooth bounded projection operator

This PR adds JopClampC1, a nonlinear Jet operator for pointwise bounded projection with consistent forward, Jacobian, and adjoint-Jacobian actions.

• Acts like a hard clamp outside [lo, hi]
• Acts like the identity in the interior
• Replaces the sharp clamp corners with a cubic transition layer of width δ = transition * (hi - lo) near each bound, making the operator C1

Why this is useful:

• preserves practical bound enforcement,
• avoids derivative jumps from hard clamping,
• gives cleaner and more stable linearization behavior for optimization and testing.

The accompanying tests cover:

• forward correctness,
• Jacobian linearity and dot-product consistency,
• O(μ) and O(μ²) linearization rates in the smooth case,
• and the expected loss of smooth asymptotics for hard-clamp boundary crossing.

[codecov]

Codecov Report

❌ Patch coverage is 91.93548% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.73%. Comparing base (51d413c) to head (c36b1a9).

Files with missing lines	Patch %	Lines
src/jop_clamp_c1.jl	91.93%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #47      +/-   ##
==========================================
- Coverage   95.94%   95.73%   -0.22%     
==========================================
  Files          40       41       +1     
  Lines        1086     1148      +62     
==========================================
+ Hits         1042     1099      +57     
- Misses         44       49       +5     

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[jkwashbourne-oss]

can you fix the coverage issue? might be missing a test?

[nmbader]

no missing tests just miscounting from codecov that misses lines of loop end when simd is used