Port SQLPage to sqlx 0.9 with external SQL Server and ODBC drivers

Summary

This draft PR ports SQLPage away from the sqlx-oldapi compatibility crate and onto the current sqlx crate. SQL Server and ODBC support move to the external sqlx-sqlserver and sqlx-odbc crates.

The important API change is that sqlx::Any in sqlx 0.9 no longer preserves the driver-specific row/type information SQLPage needs for JSON conversion, CSV import, DB-backed files, and backend-specific behavior. The implementation therefore replaces SQLPage's central AnyPool usage with a small SQLPage-owned backend enum and dispatches to native sqlx pool/connection types.

Checklist

• Switch dependencies from sqlx-oldapi to sqlx 0.9, sqlx-sqlserver, and sqlx-odbc.
• Replace sqlx::any::AnyKind with a SQLPage-owned backend kind enum.
• Replace AnyPool and PoolConnection<Any> with SQLPage-owned pool and connection enums.
• Rewrite database URL/connection-string parsing, including password override behavior.
• Preserve SQLite custom setup: extensions, NOCASE collation, and Unicode upper/lower support where supported by the new API.
• Preserve ODBC custom setup: direct connection strings, batch size, unbounded column size, and DBMS-name detection.
• Rewrite query execution so parameters are bound through native backend query types.
• Preserve SQLite response streaming: statement execution now forwards a boxed per-statement stream and does not collect result sets into memory before yielding rows to the renderer/browser.
• Rewrite row-to-JSON conversion for native backend row types instead of AnyRow.
• Preserve PostgreSQL advanced type handling without routing through Any.
• Preserve ODBC decimal/numeric JSON shape by dispatching from column metadata and decoding DECIMAL/NUMERIC text-buffer values as JSON numbers instead of strings, including Oracle ODBC's leading-dot decimal formatting.
• Recheck SQL Server advanced type support in the external sqlx-sqlserver crate and use the new 0.0.3 typed decoders for decimal/money, date/time, datetimeoffset, and uniqueidentifier values. No upstream issue needed.
• Recheck SQL Server text decoding behavior in sqlx-sqlserver; opened upstream issue Decode SQL Server VARCHAR using column collation/codepage instead of UTF-8 lovasoa/sqlx-sqlserver#1 for non-UTF-8 VARCHAR decoding. SQLPage's MSSQL CSV fixture uses NVARCHAR literals and character-code construction for Unicode/quoted text until that is fixed upstream.
• Fix the SQL Server advanced forms example survey page to use T-SQL JSON parsing and string concatenation.
• Fix MySQL-backed example SQL for MySQL string concatenation and reserved table names.
• Update CSV import, keeping PostgreSQL COPY and using normal inserts for other backends.
• Update DB-backed filesystem query execution.
• Update migrations, including a clear error for ODBC user migrations because sqlx-odbc does not implement migration support.
• Update telemetry pool metrics for the new pool enum.
• Update placeholder parsing/tests to use the SQLPage backend kind.
• Enable vendored OpenSSL for sqlx-sqlserver/native-tls and install full Perl in the Docker builder so cross-compiled images can build OpenSSL from source.
• Add examples-folder smoke coverage so every top-level example is either entry-page rendered locally or explicitly classified as requiring an external service stack.
• Add opt-in Postgres/MySQL example smoke coverage for examples that require those backends.
• Run example smoke coverage against local SQLite-compatible, Postgres, and MySQL examples.
• Run cargo fmt --all.
• Run cargo clippy --all-targets --all-features -- -D warnings.
• Run cargo test.

Validation

• cargo check
• cargo fmt --all
• cargo test sql_to_json
• cargo test --test examples
• SQLPAGE_TEST_EXAMPLES_POSTGRES_ADMIN_URL='postgres://root:Password123!@127.0.0.1/postgres' SQLPAGE_TEST_EXAMPLES_MYSQL_ADMIN_URL='mysql://root:Password123!@127.0.0.1/mysql' cargo test --test examples
• DATABASE_URL='mysql://root:Password123!@127.0.0.1/sqlpage' cargo test transactions::test_transaction_error
• DATABASE_URL='mysql://root:Password123!@127.0.0.1/sqlpage' cargo test sql_test_files::run_all_sql_test_files
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test
• docker build --platform linux/amd64 --build-arg TARGETARCH=amd64 --build-arg BUILDARCH=amd64 --build-arg CARGO_PROFILE=dev --target minimal . progressed past vendored OpenSSL configuration and project compilation after installing full Perl; the final mv failed because Cargo's built-in dev profile writes to debug/ while the Docker scripts expect the named profile directory used by superoptimized.
• Attempted SQL Server Docker validation with docker compose up -d mssql, but the local arm64/QEMU environment cannot start the amd64 SQL Server image (Invalid mapping of address ... reserved address space). The SQL Server example SQL was still reviewed and corrected to T-SQL.