rust: task: Mark Task methods inline

When building the kernel using the llvm-18.1.3-rust-1.85.0-x86_64
toolchain provided by kernel.org, the following symbols are generated:

$ nm vmlinux | grep ' _R'.*Task | rustfilt
... T <kernel::task::Task>::get_pid_ns
... T <kernel::task::Task>::tgid_nr_ns
... T <kernel::task::Task>::current_pid_ns
... T <kernel::task::Task>::signal_pending
... T <kernel::task::Task>::uid
... T <kernel::task::Task>::euid
... T <kernel::task::Task>::current
... T <kernel::task::Task>::wake_up
... T <kernel::task::Task as kernel::types::AlwaysRefCounted>::dec_ref
... T <kernel::task::Task as kernel::types::AlwaysRefCounted>::inc_ref

These Rust symbols are trivial wrappers around the C functions. It
doesn't make sense to go through a trivial wrapper for these functions,
so mark them inline.

[boqun: Capitalize the title, reword a bit to avoid listing all the C
functions as the code already shows them and remove the addresses of the
symbols in the commit log as they are different from build to build.]

Link: https://github.com/Rust-for-Linux/linux/issues/1145


Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Christian Schrefl <chrisi.schrefl@gmail.com>
Reviewed-by: Charalampos Mitrodimas <charmitro@posteo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Panagiotis Foliadis <pfoliadis@posteo.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250315-inline-c-wrappers-v3-1-048e43fcef7d@posteo.net