added: ManualEstimator to turn off built-in state estimation

[franckgaga]

This new StateEstimator type enables two new features:

1. using linear predictive controller with a nonlinear state estimator, to improve the accuracy of the state estimate
2. using predictive controller of this package with a state estimator from another package, for example LowLevelParticleFilters.jl.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 98.80%. Comparing base (79b35cb) to head (b86dbd7).

Files with missing lines	Patch %	Lines
src/estimator/manual.jl	94.11%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #206      +/-   ##
==========================================
- Coverage   98.81%   98.80%   -0.02%     
==========================================
  Files          25       26       +1     
  Lines        4234     4251      +17     
==========================================
+ Hits         4184     4200      +16     
- Misses         50       51       +1     

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