wip: feat: adding guarded minimum rust version checks

[dotkas]

Currently too sloppy for a real PR. Needs more investigation / thoughts.

Want the CLI to self-report the minimum supported rust version (msrv) of the generated code to the user, as well as best-effort keep that in sync automatically as dependencies gets bumped / features change over time.

[Copilot]

Pull request overview

This PR introduces an explicit, test-enforced MSRV for consumer-compiled generated code (separate from the workspace/tooling Rust version), and wires that MSRV through the CLI output, documentation, and CI so the reported floor is measured rather than merely stated.

Changes:

• Add a dedicated package.metadata.generated-code.rust-version value and surface it in the dependency report output.
• Add an msrv-check crate plus CI job to compile all committed golden files on the declared generated-code MSRV.
• Add a generated/guarded manifest flow (make update-msrv-manifest + msrv_manifest test) and document the three Rust-version concepts.

Reviewed changes

Copilot reviewed 18 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
README.md	Links to MSRV documentation and reflects the new “generated code needs Rust …” note in example output.
Makefile	Adds msrv-manifest refresh target and MSRV verification target used by CI.
examples/bookstore/README.md	Updates example sessions to include the generated-code MSRV note.
docs/msrv.md	New document describing the generator/build MSRV vs generated-code MSRV, how it’s measured, and how to raise it.
docs/configuration.md	Cross-links dependency reporting to the Rust versions/MSRV explanation.
crates/oapi-codegen/tests/support/apimodel.rs	Factors shared test-only apimodel module out for reuse by msrv-check.
crates/oapi-codegen/tests/msrv-check/src/lib.rs	New detached crate that compiles all golden outputs as the MSRV assertion.
crates/oapi-codegen/tests/msrv-check/Cargo.toml	Generated manifest for the detached MSRV-check crate (source-of-truth: dependency report).
crates/oapi-codegen/tests/msrv-check/Cargo.lock	Lockfile for deterministic MSRV-check dependency resolution.
crates/oapi-codegen/tests/msrv-check/build.rs	Build script that generates module includes for all committed golden files.
crates/oapi-codegen/tests/msrv_manifest.rs	New test to keep msrv-check/Cargo.toml in sync with the dependency report.
crates/oapi-codegen/tests/generated.rs	Switches apimodel stub to include! the shared support file.
crates/oapi-codegen/tests/fixtures/manifests/two_rust_versions.toml	Fixture to ensure generated-code MSRV parsing doesn’t fall back to [package].rust-version.
crates/oapi-codegen/tests/fixtures/manifests/generated_code_table_without_rust_version.toml	Fixture to ensure parsing stops at the next table header.
crates/oapi-codegen/src/deps.rs	Adds generated-code MSRV parsing from the crate manifest and tests for correctness.
crates/oapi-codegen/src/console.rs	Prints the generated-code MSRV alongside dependency guidance.
crates/oapi-codegen/Cargo.toml	Adds metadata table declaring the generated-code MSRV; adds crates.io metadata fields.
Cargo.toml	Declares workspace/tooling rust-version and workspace homepage.
.github/workflows/ci.yml	Adds generated-code-msrv job compiling goldens on the consumer MSRV and gates CI pass on it.