perf: use zero-copy slice for binary/hex/octal number parsing

[max-sixty]

Summary

Use .to_slice() instead of .collect::<String>() when parsing binary, hexadecimal, and octal number literals. This eliminates one allocation per literal by passing a string slice directly to i64::from_str_radix() instead of allocating an intermediate String.

The change also simplifies the code by removing an unnecessary allocation step.

Changes

// Before
.collect::<String>()
.map(move |digits| {
    i64::from_str_radix(&digits, base)

// After  
.to_slice()
.map(move |digits: &str| {
    i64::from_str_radix(digits, base)

Test plan

• All existing tests pass (task prqlc:test)
• 569 tests passing, no regressions
• Clippy clean

🤖 Generated with Claude Code