fix: infer LIMIT and OFFSET placeholder parameter types

[Probablism]

Which issue does this PR close?

• Closes Placeholder datatype not inferred after LIMIT clause #15978.

Rationale for this change

Bare placeholders used as LIMIT or OFFSET row-count expressions currently remain untyped in LogicalPlan::get_parameter_types(). DataFusion already coerces LIMIT/OFFSET row counts to Int64 during analysis, so the metadata APIs should report the same type for bare row-count placeholders.

What changes are included in this PR?

• Infer Int64 parameter fields for bare unresolved placeholders used directly as LIMIT or OFFSET expressions.
• Reuse existing expression placeholder inference before applying the LIMIT/OFFSET fallback, so nested expressions keep their local inference behavior.
• Preserve existing placeholder conflict detection.
• Add raw logical-plan and SQL/PREPARE regression tests for LIMIT/OFFSET parameter inference.

Are these changes tested?

Yes:

• cargo fmt --all -- --check
• cargo test -p datafusion-expr test_limit_
• cargo test -p datafusion-sql --test sql_integration test_infer_types_from_limit
• cargo test -p datafusion-sql --test sql_integration test_prepare_statement_infer_types_from_limit
• cargo test -p datafusion
• cargo test -p datafusion-cli
• cargo test --profile=ci --test sqllogictests
• ./dev/rust_lint.sh

Are there any user-facing changes?

Yes. LogicalPlan::get_parameter_types() and LogicalPlan::get_parameter_fields() now report Int64 for bare placeholders used directly in LIMIT and OFFSET. There are no breaking API changes.