feat(isthmus)!: make unquoted identifier casing configurable in ConverterProvider

[nielspardon]

Summary

Adds constructor-based configuration of unquoted SQL identifier casing to ConverterProvider, so that isthmus consumers can control how unquoted identifiers are cased during parsing. The default remains Casing.TO_UPPER (no behaviour change).

Previously the only way to change this was to subclass ConverterProvider and override getSqlParserConfig() — as IsthmusEntryPoint already did with an anonymous class. That workaround is now replaced by a first-class constructor parameter.

Breaking change

The SqlParser.Config-based parsing entry points (public in v0.94.0) have been removed in favour of ConverterProvider overloads:

• SubstraitSqlStatementParser.parseStatements(String, SqlParser.Config)
• SubstraitSqlToCalcite.convertQueries(String, CatalogReader, SqlParser.Config)
• SubstraitSqlToCalcite.convertQueries(String, CatalogReader, SqlValidator, RelOptCluster, SqlParser.Config)

Callers should pass a ConverterProvider (constructed with the desired Casing, or subclassed with an overridden getSqlParserConfig() for fully custom parser settings) instead of a SqlParser.Config.

Changes

ConverterProvider

• unquotedCasing is a new final field, consistent with executionBehavior
• getUnquotedCasing() — getter
• getSqlParserConfig() reads unquotedCasing instead of hard-coding Casing.TO_UPPER
• New constructors: ConverterProvider(Casing) and ConverterProvider(extensions, typeFactory, Casing) for the common cases; the existing 7-arg all-components constructor gains Casing as an 8th parameter. All narrower constructors default to Casing.TO_UPPER.
• ConverterProvider.DEFAULT — a shared constant for the default (all-system-defaults) provider, used at every call site that previously wrote new ConverterProvider().

Propagation through the pipeline

The casing setting is applied consistently across both CREATE TABLE parsing and query parsing, so that the table name stored in a NamedScan matches the configured casing end-to-end.

Class	Change
SubstraitSqlStatementParser	parseStatements(String, ConverterProvider) now owns the SqlParser instantiation directly; the SqlParser.Config overload is removed — callers needing fully custom config should subclass ConverterProvider and override getSqlParserConfig()
SubstraitSqlToCalcite	New convertQueries(sql, catalog, ConverterProvider) and convertQueries(sql, catalog, ConverterProvider, operatorTable) overloads; all internal overloads now route through ConverterProvider; the SqlParser.Config overloads are removed
SubstraitCreateStatementParser	New processCreateStatements(ConverterProvider, sql) and processCreateStatementsToCatalog(ConverterProvider, ...) overloads
SqlToSubstrait	convert(sql, catalog) now uses the ConverterProvider path; convert(sql, catalog, SqlDialect) is @Deprecated — the SqlDialect argument is ignored and it simply delegates to convert(sql, catalog)
SqlExpressionToSubstrait	Uses processCreateStatements(converterProvider, tableDef)
SubstraitToSql	No-arg constructor uses ConverterProvider.DEFAULT
IsthmusEntryPoint	Uses new ConverterProvider(unquotedCasing); anonymous ConverterProvider subclass removed
FromSql (example)	Replaces the deprecated convert(sql, catalog, SqlDialect) call with a single ConverterProvider(Casing.UNCHANGED) shared across both the schema build and the query conversion, preserving the lower-case identifiers as written

Test

UnquotedCasingTest verifies:

• The default casing is TO_UPPER and is reflected in getSqlParserConfig()
• new ConverterProvider(Casing) sets the casing correctly for all three Casing values
• End-to-end: with TO_UPPER a plan built from CREATE TABLE employees … / SELECT … FROM employees produces a NamedScan with name EMPLOYEES; with UNCHANGED it produces employees

Existing tests DdlToSubstraitConversionTest and DdlToSubstraitConversionWithOptimizationTest are updated to use the ConverterProvider API instead of the removed SqlParser.Config overloads.

Notes

For consumers who need a fully custom parser configuration beyond what ConverterProvider exposes (e.g. a different parser factory), the supported extension point is subclassing ConverterProvider and overriding getSqlParserConfig(). The SqlParser.Config overloads on SubstraitSqlStatementParser and SubstraitSqlToCalcite have been removed since they are entirely superseded by this.