perf: add missing fixed for fixed strings

[m-muecke]

• Add fixed for fixed strings
• Replace any(is.na(x)) with anyNA(x)

[gaborcsardi]

Thanks! Interestingly the difference is not very big:

❯ x <- cli:::lorem_ipsum()
❯ bench::mark(regex = strsplit(x, ""), fixed = strsplit(x, "", fixed = TRUE))
# A tibble: 2 × 13
  expression      min median `itr/sec` mem_alloc `gc/sec` n_itr  n_gc total_time
  <bch:expr> <bch:tm> <bch:>     <dbl> <bch:byt>    <dbl> <int> <dbl>   <bch:tm>
1 regex        5.86µs 7.34µs   120600.    3.46KB      0   10000     0     82.9ms
2 fixed         5.9µs 6.15µs   156167.    3.46KB     15.6  9999     1       64ms
# ℹ 4 more variables: result <list>, memory <list>, time <list>, gc <list>

[gaborcsardi]

Thanks!