Fix bug in IS method error message + documentation typos

[ishaan-arora-1]

Hey! I was going through the codebase and spotted a small bug along with some typos. Figured I'd clean them up in one go.

Bug fix

In R/importance_sampling.R, the function assert_importance_sampling_method_is_implemented() constructs an error message when an unsupported importance sampling method is passed. On line 117, implemented_is_methods is used without ():

paste0(implemented_is_methods, collapse = "', '")

Since implemented_is_methods is a function, this ends up pasting the function object itself into the error message instead of the actual method names ("psis", "tis", "sis"). The condition check on line 113 correctly calls implemented_is_methods(), so this was just missed in the message string.

Typos

While reading through the source I also noticed these scattered across the roxygen comments:

• diagnostics.R: "dependend" → "dependent", "k-ht" → "k-hat"
• loo-glossary.R: "The pages provides definitions to" → "The page provides definitions of"
• split_moment_matching.R: "log-likeliood" → "log-likelihood"
• loo_subsample.R: "subampled" → "subsampled"
• loo_compare.psis_loo_ss_list.R: "comaprison" → "comparison"
• loo_model_weights.R: "matrices or , one for each" → "matrices, one for each"
• loo-package.R: "widely application" → "widely applicable" (Watanabe 2010 reference)

I also updated the corresponding .Rd man pages to match.

Fixes #325

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.78%. Comparing base (2883f25) to head (843ec66).

Files with missing lines	Patch %	Lines
R/importance_sampling.R	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #326   +/-   ##
=======================================
  Coverage   92.78%   92.78%           
=======================================
  Files          31       31           
  Lines        2992     2992           
=======================================
  Hits         2776     2776           
  Misses        216      216           

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