Improve split statement regex, pagination and result messages

[dnlw07]

Summary

• Add src/ls/splitStatements.ts: a quote/comment-aware SQL statement
  splitter that tracks BEGIN/CASE/IF/WHILE/FOR/LOOP/REPEAT nesting depth,
  so multi-statement scripts and PL/SQL-style blocks split correctly.
• Rework src/ls/driver.ts:
  • open() connects asynchronously via callback and, if
    connectionInitSql is set on the connection, runs it once after
    connecting (e.g. SET CURRENT SCHEMA/PATH), failing loudly and
    closing the connection if the init script errors.
  • close() closes the connection asynchronously via callback instead
    of closeSync().
  • query() now splits input with splitStatements, normalizes
    CRLF/CR line endings, and distinguishes result-set statements
    (SELECT/WITH/VALUES/CALL/DESCRIBE/EXPLAIN/XQUERY) from DML/DDL,
    executing each via queryResult or prepare + executeNonQuery
    as appropriate.
  • Added pagination for a lone SELECT/WITH statement: exact
    COUNT(*) (cached per query/tab, refreshed on page 0) with a
    look-ahead fallback when the COUNT wrapper isn't accepted.
  • Richer result messaging: affected-row counts for DML/DDL, "0 rows
    returned" for empty result sets, elapsed time in all messages.
  • Removed a debug log that printed the full connection string
    (including the plaintext password) on every connect.
• Add connectionInitSql to connection.schema.json / ui.schema.json
  (rendered as a textarea in the connection form).
• Update README.md (Windows install path, issues link, expanded
  build prerequisites) and bump package.json version to 0.0.4.

Test plan

• npm run compile / tsc --noEmit passes
• Connect to a Db2 database with and without connectionInitSql set
• Run a plain SELECT and confirm pagination (next/prev page) works
• Run a multi-statement script (DDL + DML) and confirm each statement
  reports the correct affected-row message
• Run a script containing a BEGIN ... END block and confirm it is
  not split mid-block