The greedy name pre-pass asked the Yomitan backend at every Japanese
position, because a character name can begin mid-token. With the character
dictionary enabled that roughly doubled the round trips per line (measured
10 -> 21 on a 23-char line).
SubMiner generates the character dictionary, so the cached snapshots already
list every form a character entry can be matched by (term and reading). Those
forms are installed into the scan runtime once per media and the pre-pass now
probes only positions where one of them starts, compared after kana
normalization so a katakana name still matches a hiragana reading form. The
overhead drops to zero (21 -> 10, the same as with the dictionary disabled).
Fail-safe: with no candidate list (no media id, no cached snapshot, failed
install) the pre-pass keeps its exhaustive behavior, so stale character data
costs speed rather than a missing name. Halfwidth katakana positions bypass
the filter since kana normalization does not fold them.
The candidate lookup is consulted per subtitle line, so it caches its snapshot
directory signature for 5s; dictionary writes still call invalidate().
