Preserve embedded NUL bytes in TEXT values

[sbking]

Summary

sqlite3_bind_text currently passes -1 as the byte length, and the Emscripten string return conversion used by column_text also treats NUL as a terminator. As a result, TEXT values containing embedded NUL bytes are truncated in both directions.

• pass the encoded UTF-8 byte length to sqlite3_bind_text
• decode the complete sqlite3_column_bytes range while retaining Emscripten's existing UTF-8 decoding behavior
• add separate write-side and read-side regression tests, including preservation of a leading byte order mark

Testing

• focused Chrome tests before the fix: both new assertions fail independently at the embedded NUL
• focused Chrome tests after the fix: 7 passed, 0 failed
• compatibility probes preserve SQL NULL for non-string low-level bind_text inputs, leading U+FEFF, and existing malformed UTF-8 decoding
• prettier --check src/sqlite-api.js .changeset/fuzzy-spoons-smile.md
• node --check test/api_statements.js

The repository's full api.test.js exceeded Web Test Runner's file-level finish timeout on both pristine main (120 seconds) and this branch (300 seconds), so I don't have a full-suite result for either tree.

References

• SQLite's sqlite3_bind_text contract specifies that a negative byte length stops at the first NUL, while an explicit non-negative length preserves embedded NULs.
• SQLite's column-value contract defines sqlite3_column_bytes as the full UTF-8 byte length and recommends calling sqlite3_column_text before sqlite3_column_bytes.
• SQLite explicitly supports embedded NULs in stored TEXT, while documenting caveats for some SQL functions and CLI rendering.

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