fix: infer LIMIT and OFFSET parameter types

[1fanwang]

Which issue does this PR close?

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

Rationale for this change

Prepared-statement clients get no type for LIMIT/OFFSET arguments even when the query executes correctly. A later untyped occurrence can also erase an already inferred parameter type.

Prior work: #15980 and #23260.

What changes are included in this PR?

Default bare row-count parameters to Int64 only after collecting other type information. Preserve known fields and keep incomplete PREPARE signatures deferred rather than dropping unknown positions.

What is the testing strategy for this PR?

The tests plan, bind and execute real SQL, including mixed-type PREPARE statements. The same command ran on the base with the regression tests added, then on the fix, using Linux and Rust 1.98.1:

CARGO_BUILD_JOBS=2 cargo test --locked --profile ci -p datafusion \
  --test core_integration test_limit_offset_parameters \
  -- --nocapture --test-threads=1

#	Scenario	Command	Result
1	LIMIT parameter metadata	Above	None becomes Int64; the query still returns 20

Before:

assertion `left == right` failed: SELECT 20 AS value LIMIT $1
  left: {"$1": None}
 right: {"$1": Some(Int64)}

After:

parameters={"$1": Some(Int64)}
+-------+
| value |
+-------+
| 20    |
+-------+

Additional raw PREPARE output

Before:

test sql::select::test_limit_offset_parameters_prepare_execute ... Prepare: "page" []

After:

test sql::select::test_limit_offset_parameters_prepare_execute ... Prepare: "page" [Int64, Int64]

Are there any user-facing changes?

Yes. Parameter metadata supplies integer types for otherwise-untyped LIMIT/OFFSET arguments while retaining known types and field metadata.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.94%. Comparing base (5a44905) to head (7666e87).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25364      +/-   ##
==========================================
- Coverage   81.94%   81.94%   -0.01%     
==========================================
  Files        1135     1135              
  Lines      428278   428292      +14     
  Branches   428278   428292      +14     
==========================================
+ Hits       350945   350951       +6     
- Misses      56378    56384       +6     
- Partials    20955    20957       +2     

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