max_spill_size incorrect default value

[mrjsj]

Environment

Delta-rs version:
0.19.0

Binding:
Rust

Environment:

• Cloud provider: N/A
• OS: N/A
• Other: N/A

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Bug

What happened:
The default value in crates/core/src/operations/optimize.rs::OptimizeBuilder::max_spill_size should be 20 GB, but it's nearly the double, as it's set to 20 * 1024 * 1024 * 2014

What you expected to happen:
Should be: 20 * 1024 * 1024 * 1024

How to reproduce it:

More details:
I will create PR with fix

[mrjsj]

take