Guard insert placeholder zero

[Sean-Kenneth-Doherty]

Which issue does this PR close?

Fixes #22224.

Rationale for this change

EXPLAIN INSERT INTO t VALUES ($0) currently panics while inferring parameter types for INSERT VALUES. Other SQL paths already reject $0 as an invalid placeholder index, and the INSERT inference path should do the same instead of subtracting one from zero.

What changes are included in this PR?

• Adds a zero-index guard before INSERT VALUES placeholder numbers are converted to parameter vector positions.
• Aligns the INSERT VALUES error with the existing invalid-placeholder planning error.
• Adds a standalone SQL logic regression for EXPLAIN INSERT INTO ... VALUES ($0).

Are these changes tested?

Yes.

• cargo fmt --check --all
• cargo test -p datafusion-sqllogictest --test sqllogictests -- insert_values_placeholders
• cargo test -p datafusion-sql --test sql_integration test_insert_schema_errors -> 6 passed
• git diff --check origin/main...HEAD
• git diff --cached --check

Are there any user-facing changes?

Yes. INSERT ... VALUES ($0) now returns a planning error instead of panicking.

Scope note

The change is limited to INSERT VALUES placeholder type inference and the new regression coverage. I did not find any broader placeholder semantics that needed to change.

[Sean-Kenneth-Doherty]

Local validation on current head (f15210789):

• cargo test -p datafusion-sqllogictest --test sqllogictests -- insert_values_placeholders -> completed 1/1 files
• cargo test -p datafusion-sql --test sql_integration test_insert_schema_errors -> 6 passed
• cargo test -p datafusion-sql --test sql_integration params -> 35 passed
• cargo fmt --all --check -> passed
• cargo clippy -p datafusion-sql --all-targets -- -D warnings -> passed
• git diff --check origin/main...HEAD && git diff --check -> clean

The local checkout is clean after validation.