Improve Internal perf

[Hoverbear]

Thanks to a report by @jamessewell we were able to find some performance improvements which lead to us doing a bit more allocation than needed in some Internal type calls.

Using an example of

pub struct RustMaxInternal;

#[pg_aggregate]
impl Aggregate for RustMaxInternal {
    type Args = i32;
    type State = Internal;
    type Finalize = i32;
    #[inline(always)]
    fn state(
        mut current: Self::State,
        value: Self::Args,
        _fcinfo: pg_sys::FunctionCallInfo,
    ) -> Self::State {
        let inner = unsafe { current.get_or_insert_default::<i32>() };

        if *inner < value {
            *inner = value;
        };
        current
    }
    #[inline(always)]
    fn combine(
        mut first: Self::State,
        mut second: Self::State,
        _fcinfo: pg_sys::FunctionCallInfo,
    ) -> Self::State {
        let first_inner = unsafe { first.get_or_insert_default::<i32>() };
        let second_inner = unsafe { second.get_or_insert_default::<i32>() };


        if *first_inner < *second_inner {
            *first_inner = *second_inner;
        };
        first
    }
    #[inline(always)]
    fn finalize(
        mut current: Self::State,
        _direct_arg: Self::OrderedSetArgs,
        _fcinfo: pg_sys::FunctionCallInfo,
    ) -> Self::Finalize {
        let inner = unsafe { current.get_or_insert_default::<i32>() };
        *inner
    }
}

Before:

$ cargo pgx run pg14 -p pgx-tests --features pg_test --release
    Stopping Postgres v14
building extension with features `pg_test pg14`
"cargo" "build" "--package" "pgx-tests" "--release" "--features" "pg_test pg14" "--no-default-features" "--message-format=json-render-diagnostics"
   Compiling pgx-tests v0.4.0 (/home/ana/git/zombodb/pgx/pgx-tests)
    Finished release [optimized] target(s) in 11.81s

installing extension
     Copying control file to /home/ana/.pgx/14.2/pgx-install/share/postgresql/extension/pgx_tests.control
     Copying shared library to /home/ana/.pgx/14.2/pgx-install/lib/postgresql/pgx_tests.so
 Discovering SQL entities
  Discovered 332 SQL entities: 32 schemas (2 unique), 282 functions, 11 types, 1 enums, 2 sqls, 0 ords, 0 hashes, 4 aggregates
     Writing SQL entities to /home/ana/.pgx/14.2/pgx-install/share/postgresql/extension/pgx_tests--1.0.sql
    Finished installing pgx_tests
    Starting Postgres v14 on port 28814
    Re-using existing database pgx_tests
psql (14.2)
Type "help" for help.

pgx_tests=# DROP EXTENSION pgx_tests; CREATE EXTENSION pgx_tests;
DROP EXTENSION
CREATE EXTENSION
pgx_tests=# \timing
Timing is on.
pgx_tests=# SELECT RustMaxInternal(value) FROM generate_series(0, 400000) as value;
 rustmaxinternal 
-----------------
          400000
(1 row)

Time: 131.944 ms
pgx_tests=# 

After:

pgx_tests=# SELECT RustMaxInternal(value) FROM generate_series(0, 400000) as value;
 rustmaxinternal 
-----------------
          400000
(1 row)

Time: 94.889 ms

[eeeebbbbrrrr]

Please target this to the develop branch.