Fix Rust 1.82 compilation errors by upgrading PyO3 from 0.18 to 0.20

[drganjoo]

PyO3 Upgrade to Fix Compatibility with Rust 1.82

This PR addresses a compatibility issue between PyO3 0.18 and Rust 1.82, which causes compilation errors due to unexpected cfg condition names.

When compiled with Rust 1.82, the current PyO3 0.18 dependency produces errors like:

error: unexpected `cfg` condition name: `addr_of`

This error occurs because of changes in how Rust handles conditional configuration checks in newer compiler versions.

Changes in this PR:

1. Upgrades PyO3 from version 0.18 to 0.20 (the latest version compatible with pyo3-asyncio)
2. Updates generated functions to follow the required API pattern where required fields precede optional ones
3. API changes in pyo3, whereby in the new version dictionary.get_key returns a Result<Option> instead of Result in the older version.

This upgrade ensures compatibility with Rust 1.82 while maintaining all existing functionality.

Testing

1. Current protocol tests pass
2. An additional test has been included for required versus optional parameters.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[ysaito1001]

With the code changes, did executing below from smithy-rs/rust-runtime work fine (or maybe reduced error messages)?

RUSTDOCFLAGS='--cfg docsrs -Dwarnings' cargo +nightly-2025-05-04 doc --no-deps --document-private-items --all-features

which was this incantation that led to the original issue

[arielb1]

pyo3-asyncio is now https://crates.io/crates/pyo3-async-runtimes (the new crate is by the author of pyo3, the previous crate had a different author), you can update to that

[drganjoo]

pyo3-asyncio is now https://crates.io/crates/pyo3-async-runtimes (the new crate is by the author of pyo3, the previous crate had a different author), you can update to that

We'll handle the migration to pyo3-async-runtimes in a future PR. Since that change will involve several breaking API modifications, this current PR focuses specifically on removing the CI warnings to keep our build pipeline clean.

I've created a separate issue to track this upgrade: #4152

[drganjoo]

With the code changes, did executing below from smithy-rs/rust-runtime work fine (or maybe reduced error messages)?

RUSTDOCFLAGS='--cfg docsrs -Dwarnings' cargo +nightly-2025-05-04 doc --no-deps --document-private-items --all-features

which was this incantation that led to the original issue

Yes - this PR addresses all the Python-related errors. I intentionally kept these fixes separate from the other work in PR #4125 to maintain clearer change boundaries. Once this PR is merged, PR #4125 should be able to resolve the remaining warnings.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• No codegen difference in the Server Test
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

[landonxjames]

Went ahead and merged this since I am working on the next MSRV bump in #4154 and wanted to clear out these errors