Quote schema identifiers during table creation

[akshithg]

Fix a schema-creation regression introduced by #17. That change quoted schema names in table references but left CREATE SCHEMA unquoted. For a schema named MixedCase, PostgreSQL creates the schema as mixedcase, then fails when the quoted table reference looks for MixedCase.

Apply Dialect.QuoteField to the schema name in TableMap.SqlForCreate so CREATE SCHEMA and the following CREATE TABLE use the same identifier semantics. This also escapes embedded identifier delimiters in CREATE SCHEMA, addressing a remaining gap related to #16.

Add regression cases for PostgreSQL double-quote escaping and MySQL backtick escaping. The regression fails before the fix and passes afterward.

Validation passed with Go 1.27.1: go test ./..., go test -race ./..., go vet ./..., go build ./..., and git diff --check. Database integration suites also passed against PostgreSQL 17, MariaDB 10.5, and SQLite on the same source tree. Additional review checks covered IF NOT EXISTS, repeated creation, and PostgreSQL LowercaseFields.