Add balance accessor to community model

[stelmo]

/format

[github-actions[bot]]

:heavy_check_mark: Auto-formatting triggered by this comment succeeded, commited as 4f657e143170eb9c414985b003cd428f600492f9

[codecov[bot]]

Codecov Report

Base: 89.58% // Head: 89.53% // Decreases project coverage by -0.05% :warning:

Coverage data is based on head (4f657e1) compared to base (a1c2e6b). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## next #743 +/- ## ========================================== - Coverage 89.58% 89.53% -0.05% ========================================== Files 85 85 Lines 2054 2055 +1 ========================================== Hits 1840 1840 - Misses 214 215 +1 ``` | [Impacted Files](https://codecov.io/gh/LCSB-BioCore/COBREXA.jl/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LCSB-BioCore) | Coverage Δ | | |---|---|---| | [src/types/models/BalancedGrowthCommunityModel.jl](https://codecov.io/gh/LCSB-BioCore/COBREXA.jl/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LCSB-BioCore#diff-c3JjL3R5cGVzL21vZGVscy9CYWxhbmNlZEdyb3d0aENvbW11bml0eU1vZGVsLmps) | `98.21% <100.00%> (+0.03%)` | :arrow_up: | | [src/types/wrappers/EnzymeConstrainedModel.jl](https://codecov.io/gh/LCSB-BioCore/COBREXA.jl/pull/743?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=LCSB-BioCore#diff-c3JjL3R5cGVzL3dyYXBwZXJzL0VuenltZUNvbnN0cmFpbmVkTW9kZWwuamw=) | `91.89% <0.00%> (-2.71%)` | :arrow_down: | 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=LCSB-BioCore). 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=LCSB-BioCore)

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