Fix #1640: validate numeric value separator in non-root context for non-blocking parser

[seonwooj0810]

Summary

Follow-up to #1615 (which fixed the three blocking parsers) and per @cowtowncoder's comment in that PR confirming a separate fix for the non-blocking path is warranted.

The non-blocking (async) parser did not verify that numeric values are followed by a valid separator (whitespace, comma, ], }) when parsed inside an Array or Object context, silently accepting malformed inputs that blocking parsers rejected:

// Blocking parsers (fixed in #1615): correctly throw
// Async parser (this PR): previously returned VALUE_NUMBER_INT
JsonParser p = factory.createNonBlockingByteArrayParser(...);
feeder.feedInput(new byte[]{'[','1','2','3','t','r','u','e',']'}, 0, 9);
feeder.endOfInput();
p.nextToken(); // START_ARRAY
p.nextToken(); // was VALUE_NUMBER_INT, should throw StreamReadException

Root cause

Five integer-completion sites and three float-completion sites in NonBlockingUtf8JsonParserBase called _valueComplete(JsonToken.VALUE_NUMBER_*) without a separator check:

• _startPositiveNumber(int ch) — inline digit loop
• _startNegativeNumber() — inline digit loop
• _startPositiveNumber() — inline digit loop (+ sign variant)
• _finishNumberIntegralPart(...) — resumption path (chunk boundary)
• Hex number completion (via resetIntHex)
• _startFloat(...) — inline fraction/exponent loop
• _finishFloatFraction() — resumption path (fraction digits)
• _finishFloatExponent(...) — resumption path (exponent digits)

Fix

Adds _verifyNumberSeparator(int ch) to NonBlockingUtf8JsonParserBase, mirroring the same method added to the three blocking parsers in #1615. For root context it delegates to the existing _verifyRootSpace(ch); for non-root context it validates the separator is one of \t\r\n,]} (or a comment-start character if the respective feature is enabled), consistent with the blocking-parser behavior.

All 8 completion sites now call _verifyNumberSeparator(ch) before _valueComplete(...).

Testing

• New test class AsyncNumberSeparator1640Test covering int, float-fraction, and float-exponent mangled cases across bytesPerRead values of 90, 3, and 1 (to exercise both inline and resumption paths).
• AsyncTokenBranchNumberErrorTest.mangledNonRootInts in tofix/ now passes; removed its @JacksonTestFailureExpected annotation. The mangledNonRootFloats test remains in tofix/ (the 'f'/'d' suffix case still uses a dedicated code path with a different error message).
• Full test suite: 1813 tests, 0 failures, 0 errors.

Fixes #1640

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