Resolving CRAN checks

[jzwart]

• Modernized inst/CITATION to current bibentry() style to resolve CRAN NOTE about old-style citation entries.
• Fixed Rd cross-references by adding package-qualified anchors for functions in rLakeAnalyzer.
• Regenerated documentation with roxygen2 7.3.3; updated RoxygenNote and rebuilt NAMESPACE.
• Refreshed package-level help (R/LakeMetabolizer-package.R) with updated author/maintainer text.
• DESCRIPTION maintenance: bumped version to 1.5.6 and standardized Maintainer name.
• Other minor housekeeping

[jzwart]

Pushed and accepted at CRAN https://cran.r-project.org/web/packages/LakeMetabolizer/index.html . Self-merging and releasing v1.5.6