Lockfile bugfix and better-looking graphs

Version 7.12.3

Bug fixes

• cached_planned() and cached_unplanned() now work with non-standard cache locations (#1268, @plebejer).
• Set use_cache to FALSE more often (#1257, @plebejer).
• Use namespaced function calls in mtcars example instead of loading packages.
• Replace the iris dataset with the airquality dataset in all documentation, examples, and tests (#1271).
• Assign functions created with code_to_function() to the proper environment (#1275, @robitalec).
• Store tracebacks as character vectors and restrict the contents of error objects to try to prevent accidental storage of large data from the environment (#1276, @billdenney).
• Strongly depend on tidyselect (#1274, @dernst).
• Avoid txtq lockfiles (#1232, #1239, #1280, @danwwilson, @pydupont, @mattwarkentin).

New features

• Add a new drake_script() function to write _drake.R files for r_make() (#1282).

Enhancements

• Deprecate expose_imports() in favor of make(envir = getNamespace("yourPackage") (#1286, @mvarewyck).
• Suppress the message recommending r_make() if getOption("drake_r_make_message") is FALSE (#1238, @januz).
• Improve the appearance of the visNetwork graph by using the hierarchical layout with visEdges(smooth = list(type = "cubicBezier", forceDirection = TRUE)) (#1289, @mstr3336).