Ensure compatibility w/quanteda v1.0

[kbenoit]

Makes cast_dfm() and tidy.dfm[Sparse]() compatible with quanteda v0.99.12 and with the upcoming quanteda v1.0 release, and fixes some tests.

In v1.0 (and in the current quanteda master >= v0.9.9000), the dfm structure has been simplified to just dfm, instead of dfmSparse and dfmDense. Methods to check and to coerce the object class exist as is.dfm() and as.dfm().

[codecov-io]

Codecov Report

Merging #87 into master will decrease coverage by 0.03%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##           master      #87      +/-   ##
==========================================
- Coverage    82.5%   82.46%   -0.04%     
==========================================
  Files          10       10              
  Lines         360      365       +5     
==========================================
+ Hits          297      301       +4     
- Misses         63       64       +1

Impacted Files	Coverage Δ
R/sparse_tidiers.R	100% <ø> (ø)	⬆️
R/stm_tidiers.R	92.15% <50%> (ø)	⬆️
R/sparse_casters.R	90.66% <83.33%> (-0.77%)	⬇️

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[github-actions]

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