#16: own stack values in consuming iterator

[GHX5T-SOL]

Fixes #16.

Summary:

• implement IntoIterator for Stack so consuming iteration owns the fixed array
• remove the raw pointer read loop from IntoIter::next() and copy values directly by index
• update the iterator regression to verify ordered collected values

Validation:

• cargo test --all-features -> 23 unit tests and 2 doctests passed on current master before this patch, confirming Baseline build is red on master: #[must_use] on trait-impl methods and elided-lifetime warnings now errors under stable rustc #70 no longer reproduces locally with rustc 1.94.1.
• cargo --color=never fmt --check -> passed
• cargo --color=never test --all-features -> 23 unit tests and 2 doctests passed
• cargo --color=never test --release --all-features -> 23 unit tests and 2 doctests passed
• cargo --color=never doc --no-deps -> passed
• git diff --check -> passed
• git diff | gitleaks stdin --redact --no-banner --exit-code 1 -> no leaks found

Not run locally:

• cargo clippy: this environment does not have the Cargo clippy subcommand installed.
• rustup run nightly cargo bench: rustup is not installed here, so the official nightly benchmark command could not be run locally.