Refactor LockedAmplitude and ShapedAmplitude

[goerz]

Both of these amplitudes could be made more flexible by getting rid of the type hierarchy that distinguished between, e.g., ShapedContinousAmplitude and ShapedPulseAmplitude. The shape and control can now be vectors or functions independently of each other. This enables substituting optimized pulses into existing amplitudes, among other benefits.

[Copilot]

Pull request overview

This PR refactors the amplitude layer to remove the old Locked* / Shaped* subtype split and instead represent amplitudes as parametric wrappers whose shape and control can independently be callables or discretized vectors. In the broader codebase, this sits at the control/amplitude boundary used by generator evaluation and propagation.

Changes:

• Replaces the previous LockedAmplitude and ShapedAmplitude type hierarchies with parametric structs and updated evaluate/substitute methods.
• Adds support for mixed ShapedAmplitude forms where only the control or only the shape is vector-backed.
• Expands amplitude tests to cover mixed shape/control combinations and substitution of a callable control with a discretized vector.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/amplitudes.jl	Refactors amplitude representations, constructors, substitution, display, and evaluation dispatch.
test/test_amplitudes.jl	Adds regression coverage for mixed ShapedAmplitude modes and substitution behavior.

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[codecov]

Codecov Report

❌ Patch coverage is 97.61905% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.5%. Comparing base (df3491e) to head (952dd50).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
src/amplitudes.jl	97.5%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #110     +/-   ##
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+ Coverage    90.4%   90.5%   +0.2%     
========================================
  Files          37      37             
  Lines        2615    2661     +46     
========================================
+ Hits         2362    2407     +45     
- Misses        253     254      +1     

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