Use String#chars + Array#map instead of String#each_char + Array#<<

[gonzedge]

... during Rambling::Trie#create because this benchmark says it is faster (captured as the ips:each_char_shovel_vs_chars_map):

ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-darwin23]
Warming up --------------------------------------
    each_char and <<    63.994k i/100ms
           chars map    83.503k i/100ms
Calculating -------------------------------------
    each_char and <<    615.709k (± 5.7%) i/s    (1.62 μs/i) -      3.072M in   5.006314s
           chars map    814.335k (± 2.8%) i/s    (1.23 μs/i) -      4.092M in   5.028563s

Comparison:
           chars map:   814335.0 i/s
    each_char and <<:   615708.6 i/s - 1.32x  slower

Result:

 ==> Creation - `Rambling::Trie.create`
 5 iterations -
-                                5.181516   0.113003   5.294519 (  5.296937)
+                                4.751531   0.114047   4.865578 (  4.866892)

[codeclimate]

Code Climate has analyzed commit 71d8cb5 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (95% is the threshold).

This pull request will bring the total coverage in the repository to 100.0% (0.0% change).

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