Fix two stack overflows and an ignore token counted twice

[DmitrySharabin]

Fix two stack overflows and a doubled ignore token in $inner embedding, found during a cold review of #4110/#4112/#4114 as one change.

• embed and insertTokens both call splice(start, n, ...items) with an array as long as the inner token stream — any $inner language overflows the call stack past ~460KB of input, where v2 was fine. Both now go through replaceRange() (slice, truncate, push).
• A selector naming both :text and a root-level ignore* token fed that token's text to the inner language twice, and the second copy changed how the first one parsed. Not reachable from a shipped grammar, but ignore* tokens are documented as dissolved into :text.
• token-stream.js: split halves no longer share the original's alias array, insertTokens throws instead of silently dropping text on non-ascending offsets, and splitTokenStream's isolation claim now matches what it actually does.

10253 passing / 1 pre-existing pending / 0 failing. lint:ci, tsc, and tsc -p tests/tsconfig.json all clean. Each fix is mutation-pinned — reverting the guard fails exactly one test.

file	+	−
tests/core/registry.js	35	0
tests/core/token-stream.js	28	1
src/util/token-stream.js	18	2
tests/core/embedding.js	10	0
src/core/tokenize/embed.js	3	3

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