tests: o200k tokenizer coverage, no model download

tests/tok_o200k_tiny.json is a synthetic byte-level BPE (274 vocab, a
few KB) whose Split regex is the o200k pattern; expected ids in
tok_o200k_cases.txt were generated by HF tokenizers on that same file.
test_tok_o200k (in TEST_BINS) scores 40/40 encode + 40/40 round-trip:
case-transition splits, contractions, digit groups, the [\r\n/]* tail,
whitespace branches, CJK/Greek/Cyrillic, added-token atomicity.

The cl100k path is untouched by construction — dispatch requires
\p{Lu} in the tokenizer's own Split pattern, which cl100k lacks — and
stays covered by the GLM oracle (verified on this branch: 32/32).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

c/tests/tok_o200k_cases.txt

@@ -0,0 +1,40 @@
+hello world	259,32,119,111,114,263
+HelloWorld	72,101,257,111,262
+XMLHttpRequest	88,77,76,72,116,116,112,82,101,113,117,101,115,116
+helloWORLDhello	259,87,79,82,76,68,259
+dog's	100,111,103,270
+DON'T	68,79,78,39,84
+don't	100,111,110,39,116
+I'll've	73,39,257,39,118,101
+O'Brien	79,39,66,114,105,101,110
+the theatre	265,32,116,256,97,116,114,101
+12345	268,52,53
+a1b22c333d4444	97,49,98,50,50,99,51,51,51,100,52,52,52,52
+3.14	51,46,49,52
+http://x.com/a/b	104,116,116,112,58,47,47,120,46,99,111,109,47,97,47,98
+path/to/file	112,97,264,47,116,111,47,102,105,108,101
+a//b///c	97,47,47,98,47,47,47,99
+!!\r\n//x	33,33,13,10,47,47,120
+one\ntwo\r\nthree	111,110,101,10,116,119,111,13,10,264,114,101,101
+  \n  x	32,32,10,32,32,120
+   	32,32,32
+a  b   c	97,32,32,98,32,32,32,99
+tab\there	116,269,9,256,114,101
+Café	67,97,102,101,204,129
+naiveBayes	110,97,105,118,101,66,97,121,101,115
+Éclair	195,137,99,108,97,105,114
+北京大学	229,140,151,228,186,172,229,164,167,229,173,166
+ΑΒαβ	206,145,206,146,206,177,206,178
+Иван	208,152,208,178,208,176,208,189
+ẞßscharf	225,186,158,195,159,115,99,104,97,114,102
+i̇stanbul	105,204,135,115,116,97,110,98,117,108
+hello<|endoftext|>world	259,274,119,111,114,263
+<|message_user|>hi	275,104,105
+mixedCASEand123	109,105,120,101,100,67,65,83,69,97,110,100,268
+'s	270
+ 's	32,39,115
+A	65
+aB	97,66
+Ab	65,98
+AB	65,66
+ab	269