Extract SqliteRealText from LibsqlResultSet #198

Goal

Move the SQLite REAL text formatter out of LibsqlResultSet. It is a 258-line fixed-point port of SQLite's printf("%!.17g"), all private static, with two call sites and no cursor state.

Depends on

None. This is the first pass in the LibsqlResultSet chain. The later passes in the chain are blocked by it because they edit the same file.

Pin

LibsqlResultSetRealTextTest covers canonical form, scale, repeated reads, fixed-notation bounds, and bytes. LibsqlResultSetTest covers integral truncation and BLOB-as-text.

Scope

• Create SqliteRealText with static String format(double), the four power tables, and the private fixed-point helpers moved verbatim (LibsqlResultSet 187 to 444).
• Point getString (line 181) and getBytes (line 641) at it.

Preserve

• The algorithm and tables byte for byte. Do not substitute BigDecimal.toPlainString, Double.toString, or String.format.
• Negative zero renders 0.0. Exponents render signed and zero padded to two digits. NaN renders NaN.
• Fixed notation applies when the decimal exponent is between -4 and 16.

Acceptance

• SqliteRealText.java exists and holds the moved code unchanged.
• LibsqlResultSet.java is under 1250 lines.
• ./mvnw -pl libsql-jdbc -am test green with no assertion edited.
• ./mvnw spotless:check green.