Set number of nonzeros in Hessian of the residual to 0

[tmigot]

Close #78

[codecov[bot]]

Codecov Report

Base: 90.50% // Head: 90.50% // No change to project coverage :thumbsup:

Coverage data is based on head (06b3e23) compared to base (8fb497e). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #80 +/- ## ======================================= Coverage 90.50% 90.50% ======================================= Files 5 5 Lines 295 295 ======================================= Hits 267 267 Misses 28 28 ``` | [Impacted Files](https://codecov.io/gh/JuliaSmoothOptimizers/BundleAdjustmentModels.jl/pull/80?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers) | Coverage Δ | | |---|---|---| | [src/BundleAdjustmentNLSFunctions.jl](https://codecov.io/gh/JuliaSmoothOptimizers/BundleAdjustmentModels.jl/pull/80?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers#diff-c3JjL0J1bmRsZUFkanVzdG1lbnROTFNGdW5jdGlvbnMuamw=) | `96.26% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers)

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