Kalman performance tweaks

[jlperla]

This prepares things to have a preallocated cache and implements things inplace where possible.

[coveralls]

Pull Request Test Coverage Report for Build 1854604071

• 136 of 137 (99.27%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.07%) to 84.097%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/kalman.jl	136	137	99.27%
<!--	Total:	136	137	99.27%	-->

Totals
Change from base Build 1842991448:	3.07%
Covered Lines:	312
Relevant Lines:	371

---

💛 - Coveralls

[codecov[bot]]

Codecov Report

Merging #43 (7b662fb) into main (b06d704) will increase coverage by 3.06%. The diff coverage is 99.27%.

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
+ Coverage   81.02%   84.09%   +3.06%     
==========================================
  Files           8        8              
  Lines         311      371      +60     
==========================================
+ Hits          252      312      +60     
  Misses         59       59              

Impacted Files	Coverage Δ
src/DifferenceEquations.jl	25.00% <ø> (ø)
src/kalman.jl	99.34% <99.27%> (+0.42%)	:arrow_up:

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[coveralls]

Pull Request Test Coverage Report for Build 1854604071

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 136 of 137 (99.27%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.1%) to 84.097%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/kalman.jl	136	137	99.27%
<!--	Total:	136	137	99.27%	-->

Totals
Change from base Build 1842991448:	3.1%
Covered Lines:	312
Relevant Lines:	371

---

💛 - Coveralls