Add fallback equality on `noAuth` scheme ID (#4232)

## Motivation and Context
Implements fallback equality for no auth `AuthSchemeId` so that
`AuthSchemeId::from("no_auth")` (legacy) and
`AuthSchemeId::from("noAuth")` (updated) should be treated as
equivalent.

## Description
In #4203, the internal raw strings of pre-defined `AuthSchemeId` were
updated to better align with the Smithy spec
([discussion](https://github.com/smithy-lang/smithy-rs/pull/4203#discussion_r2198206822)).
Acknowledging that this was a breaking change and that customers should
not rely on these internal representations, we did receive reports of
issues related to this update. After discussion, we proceeded with
implementing fallback equality for no auth scheme ID to allow for a
safer rollout.

## Testing
- Added unit tests for manually implemented traits for `AuthSchemeId`,
`PartialEq`, `Hash`, and `Ord`
- Added an auth scheme preference test to verify the legacy `no_auth` is
supported

## Checklist
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- [x] For changes to the smithy-rs codegen or runtime crates, I have
created a changelog entry Markdown file in the `.changelog` directory,
specifying "client," "server," or both in the `applies_to` key.
- [x] For changes to the AWS SDK, generated SDK code, or SDK runtime
crates, I have created a changelog entry Markdown file in the
`.changelog` directory, specifying "aws-sdk-rust" in the `applies_to`
key.

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