fix(sqlfmt): validate indent_count in SqlToStringFormat

[G4G4N]

… (#157)

Summary

Fixes #157 by validating indent_count in SqlToStringFormat so negative values can’t create invalid state or odd formatting behavior (e.g., in separator() which uses range(self.indent_count + cnt)).

Changes

• pylegend/core/database/sql_to_string/config.py
• Validate indent_count in init and raise a clear ValueError for negative inputs.

Rationale

• Fail fast at object creation.
• Prevents subtle bugs from negative indentation while keeping all valid usages untouched.

Backward Compatibility

• No behavior changes for non-negative values.
• Calling code that previously passed negatives will now raise ValueError (intended safeguard).

Test Plan

• Valid: 0, 1, 5, 10 → object constructs and methods behave as before.
• Invalid: -1, -10 → ValueError with helpful message.

All tests pass locally.

[linux-foundation-easycla]

• ✅login: G4G4N / name: G4G4N / (7271a3d)

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