Allows quotes to be used in string default values. Currently, using default: "test \"foo\" bar" leads to code that fails to compile. This patch puts all string literals in r#""#, solving the issue.

Depends on:

• [Rust-Axum] Dynamically set the types of integer literals #20133
• [Rust-Axum] Fix: handling non-lowercase Header in Request/Response #20178

Samples will be updated when they merge, but they should not have any merge conflicts.

# Command used to update the samples
mvn clean &&
./bin/generate-samples.sh bin/configs/manual/rust-axum-* &&
mvn integration-test -f samples/server/petstore/rust-axum/pom.xml

@linxGnu @wing328

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request, and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples, as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
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