[BUG] Apply the portable numeric contract to query literals and parameters

Bug description

Portable query numeric literals and parameters can bypass a common numeric boundary in two independent ways:

1. ExpressionParser.toLiteral(...) converts decimal literals with Double.parseDouble(...) and parses integral literals as Integer/Long. Precision may be lost before validation, and an integer outside the long range can escape as an unnormalized parse failure.
2. DefaultMulticloudDbClient.isLegacyExpression(...) treats an expression() value beginning with SELECT, containing :, or beginning with # as an opaque provider expression. That path bypasses portable parsing, capability checks, validation, and parameter normalization. Explicit native passthrough already exists as nativeExpression().

This predates #105 and should be fixed separately from partial update.

Provider

• Azure Cosmos DB
• Amazon DynamoDB
• Google Cloud Spanner
• Not provider-specific

Reproduction steps

1. Submit a portable expression containing a high-precision decimal or an integral literal outside the signed-64-bit range.
2. Compare it with the same value supplied as a parameter.
3. Submit an otherwise portable expression() containing one of the legacy heuristic tokens.
4. Observe that the requests do not consistently traverse the same parser/validator/translator path.

Expected behaviour

expression() always uses the portable pipeline. Numeric literals retain their source precision until the shared numeric contract validates/canonicalizes them. Only nativeExpression() performs provider-native passthrough.

Actual behaviour

Numeric literals are eagerly narrowed, and the legacy heuristic silently sends some expression() requests directly to a provider.

Acceptance criteria

• Numeric literal text is parsed without pre-validation precision loss.
• Literal and parameter values use the same portable numeric rules and structured errors.
• Any value-changing normalization follows the shared warning policy.
• expression() never silently becomes a native expression.
• nativeExpression() remains the explicit provider-specific escape hatch.
• Parser and cross-provider translation tests cover decimal precision, range boundaries, and legacy-token cases.

Additional context

Related umbrella issues: #37 and #64.

Start by reading ExpressionParser.toLiteral(...) and DefaultMulticloudDbClient.isLegacyExpression(...), then trace how portable expressions reach validation and provider translation. Run or extend the parser and cross-provider translation tests for decimal precision, range boundaries, parameters, and legacy-token cases. Done means expression() follows the portable path while nativeExpression() remains the explicit passthrough.