Adding the inverse tool FEObservationOperator

[ConnorMallon]

Adding the differentiable FEObservationOperator object that efficiently evaluates FEFunctions at a set of observation points.

[codecov]

Codecov Report

❌ Patch coverage is 67.64706% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.96%. Comparing base (1df55b8) to head (56d7632).

Files with missing lines	Patch %	Lines
src/Inverse/FEObservationOperators.jl	67.32%	33 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1217      +/-   ##
==========================================
- Coverage   89.04%   88.96%   -0.08%     
==========================================
  Files         213      215       +2     
  Lines       27529    27631     +102     
==========================================
+ Hits        24513    24582      +69     
- Misses       3016     3049      +33     

Flag	Coverage Δ
drivers	0.00% <0.00%> (ø)
extensions	0.00% <0.00%> (ø)
tests	88.96% <67.64%> (-0.08%)	⬇️

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[Copilot]

Pull request overview

Adds a new Inverse submodule to Gridap that introduces a differentiable FEObservationOperator for evaluating FE functions at arbitrary observation points, and wires it into the package exports and dependencies.

Changes:

• Added Inverse module with FEObservationOperator implementation and ChainRulesCore rrule.
• Exposed FEObservationOperator through Exports.jl and loaded the new module from src/Gridap.jl.
• Added ChainRulesCore dependency and introduced initial tests for the operator/adjoint.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
test/InverseTests/runtests.jl	New test entrypoint for inverse-related tests.
test/InverseTests/InverseTests.jl	Adds an adjoint check for FEObservationOperator via finite differences.
src/Inverse/Inverse.jl	Introduces the Inverse submodule, imports, and exports for inverse tooling.
src/Inverse/FEObservationOperators.jl	Implements SequentialFEObservationOperator, its evaluation, and rrule pullbacks.
src/Gridap.jl	Loads the new Inverse submodule.
src/Exports.jl	Publishes FEObservationOperator from Inverse.
Project.toml	Adds ChainRulesCore to deps/compat.

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[Copilot]

SequentialFEObservationOperator leaves cells_w_points and cache untyped, which makes these fields Any and can introduce type instability and dynamic dispatch in a performance-sensitive operator. Consider adding concrete field types (or additional type parameters) for these fields (e.g. cells_w_points::AbstractVector{<:Integer} / Vector{Int32} and cache::NTuple{4,Any} or a fully-parametric cache type).