Refactor RequestChecksumInterceptor into distinct interceptors

[ysaito1001]

Motivation and Context

This PR breaks up RequestChecksumInterceptor into two interceptors: RequestChecksumInterceptor and AwsChunkedContentEncodingInterceptor with additional code restructuring to support the upcoming aws-chunked content encoding enhancement.

Description

RequestChecksumInterceptor previously handled two distinct responsibilities:

1. Adding checksums (body or trailer)
2. Applying aws-chunked content encoding

This refactor extracts the second responsibility (aws-chunked logic) into AwsChunkedContentEncodingInterceptor, aiming to enable it via the dedicated trait when available in Smithy.

In addition, both interceptors now wrap bodies in modify_before_transmit instead of modify_before_signing per design requirements.

Tips for merging to feature/http-1.x

This refactor reluctantly adds http_0x constructs that will conflict with feature/http-1.x. Update these files when merging:

• aws-inlineable/src/http_request_checksum.rs - Apply same 1.x updates as done in branch (note: test_checksum_body_is_retryable was removed as it tested a utility only used in streaming cases against non-streaming bodies)
• aws-inlineable/src/aws_chunked.rs - Use 1.x for header names, values, and body trait methods in unit tests, as in http_request_checksum.rs
• aws/rust-runtime/aws-runtime/src/content_encoding.rs - Needs 1.x updates

    fn size_hint(&self) -> http_body_1x::SizeHint {
        http_body_1x::SizeHint::with_exact(self.encoded_length())
    }

to

    fn size_hint(&self) -> http_body_1x::SizeHint {
        http_body_1x::SizeHint::with_exact(self.options.encoded_length())
    }

because the .encoded_length() method has been moved from AwsChunkedBody to AwsChunkedBodyOptions (due to the content-length header needing encoded length during signing but body creation deferred to
modify_before_transmit)

Testing

• CI

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[github-actions]

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[landonxjames]

Looks good, a few questions, but no blockers

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A new generated diff is ready to view.

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

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[github-actions]

A new generated diff is ready to view.

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

A new doc preview is ready to view.