run_batch should return Err instead of calling process::exit(1)

[ndenev]

Summary

run_batch() calls std::process::exit(1) on query failure instead of returning an error, even though the function signature is Result<()>.

Affected code

• src/main.rs (run_batch, error branch in query loop)

Why this is a problem

1. Breaks function contract: run_batch is modeled as fallible (Result) but exits process directly.
2. Skips normal drop/unwind path: process::exit bypasses standard Rust cleanup semantics.
3. Prevents centralized error handling: caller (main) cannot intercept/format/classify batch errors consistently.
4. Hurts composability/testability: impossible to reuse run_batch safely from other call sites.

Current behavior

Inside run_batch query loop:

• on Err(e) from execute_sql_to_strings, it prints error and calls std::process::exit(1).

Proposed fix

• Replace direct process exit with error propagation:
  • return Err(anyhow::anyhow!("Error executing query: {}", e));
• Let top-level main own process exit policy.

Optional follow-up

• Add a --keep-going mode for file-based multi-statement execution if desired.

Test coverage to add

1. Batch file with one valid and one invalid statement:
   • verify non-zero process exit at top-level
   • verify error message
   • verify no hard exit inside run_batch
2. Ensure error propagation path is exercised from main.