rust: pin-init: bump minimum Rust version to 1.82

rust: pin-init: bump minimum Rust version to 1.82

Following the kernel minimum version bump in commit f32fb9c58a5b ("rust:
bump Rust minimum supported version to 1.85.0 (Debian Trixie)"), bump
pin-init's minimum Rust version to 1.82.

This removes the `lint_reasons` feature which is stabilized in 1.81 and the
`raw_ref_ops` and `new_uninit` features which are stabilized in 1.82.

Given we do not use any features that are stabilized in 1.82..=1.85 range,
and pin-init crate is useful for other projects which may have their own
MSRV requirements, the minimum version is not straightly bumped to 1.85.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Link: https://patch.msgid.link/20260428-pin-init-sync-v1-2-07f9bd3859fb@garyguo.net
Signed-off-by: Gary Guo <gary@garyguo.net>