Add opt-in domain-based CLR type mapping (boolean/guid)

[sencagri]

PR review for #1266 (proposal). Restores IBProvider-style behaviour for codebases that store booleans as SMALLINT and guids as CHAR(16) OCTETS behind named domains.

Connection string keys (both default to empty - feature is fully off when unset; no extra catalog query, no DbField allocation change):

boolean domains = D_BOOL%,IS_%
guid domains = D_GUID%

Patterns use SQL LIKE syntax. Matching is case-insensitive against RDB$FIELD_SOURCE; system domains (RDB$*) are never matched.

Design

• RawDbDataType vs DbDataType. DbField gains RawDbDataType (the actual SQL/wire type, computed from sqltype/subtype/length/charset as before) and OverrideDataType (CLR-level reporting only). DbDataType returns the override when set, otherwise RawDbDataType. All wire serialisation paths (GdsStatement.WriteRawParameter / ReadRawValue, XsqldaMarshaler, DbValue.GetBytes, DbField.FixNull) explicitly use RawDbDataType so the override cannot leak into the protocol layer.

• DomainNameResolver. Per-FbConnectionInternal cache of (relation, field) -> domain name. Populated lazily on Prepare via a single SELECT on RDB$RELATION_FIELDS (one round-trip per batch of unseen columns). Guarded by an _isResolving flag so its own internal query cannot recurse. Negative entries are cached so a missing or failed lookup does not retry every prepare. Fetch failures are swallowed (best-effort): an opt-in feature must never break user's normal queries.

• Parameter binding. FbCommand.NormalizeDomainParameterValue converts bool inputs to the underlying numeric wire type (SmallInt/Integer/ BigInt/Numeric/Decimal) using RawDbDataType, so callers can pass true or false to a SMALLINT-backed boolean column directly. Guid handling reuses the provider's existing CHAR(16) OCTETS <-> Guid path.

• DbValue.GetBoolean. Tightened from Convert.ToBoolean to explicit short/int/long/decimal -> bool with a fallback, so reading a SMALLINT with a Boolean override is safe and culture-independent.

Opt-out path

When neither connection-string key is set,
ConnectionString.HasDomainTypeMappings is false and FbCommand.Prepare returns before touching the resolver. RDB$RELATION_FIELDS is never queried, no per-field state changes, behaviour is identical to master.

Tests

• DomainPatternListTests - 12 unit tests for LIKE pattern parsing (escape handling, case-insensitivity, RDB$ exclusion, edge cases).
• DomainTypeMappingTests - 12 integration tests covering schema-level reporting, parameter round-trip (bool -> SMALLINT -> bool), guid round-trip, NULL handling, non-matching patterns staying as raw types, DataAdapter round-trip, GetSchemaTable, and resolver caching / re-entry.
• ConnectionStringTests - parsing and builder coverage for the two new keys.

Compatibility

No breaking changes. Public API surface adds two properties on FbConnectionStringBuilder (BooleanDomains, GuidDomains) and is backward-compatible at the wire level.