feat(expr): add pg_sleep function

[wangrunji0408]

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What's changed and what's your intention?

This PR adds pg_sleep and pg_sleep_for function. The #[function] macro now accepts async fn.

#[function("pg_sleep(float64)", volatile)]
async fn pg_sleep(second: F64) {
    tokio::time::sleep(Duration::from_secs_f64(second.0)).await;
}

Note that both functions return void. However, we don't have void type yet. So we make them return a null value of type int for now, as both null and void appear empty in psql. This may be corrected in the future.

We also introduced a volatile flag in #[function] macro to mark a function impure. Currently it is just a marker and has no effect. In the future, the frontend may use this to determine the purity of the function.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features Sqlsmith: Sql feature generation #7934).
• My PR contains breaking changes. (If it deprecates some features, please create a tracking issue to remove them in the future).
• All checks passed in ./risedev check (or alias, ./risedev c)
• My PR changes performance-critical code. (Please run macro/micro-benchmarks and show the results.)

• My PR contains critical fixes that are necessary to be merged into the latest release. (Please check out the details)

Documentation

• My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)

Release note

Add 2 functions:

pg_sleep ( double precision )
pg_sleep_for ( interval )

pg_sleep makes the current session's process sleep until the given number of seconds have elapsed. Fractional-second delays can be specified.
pg_sleep_for is a convenience function to allow the sleep time to be specified as an interval.

see https://www.postgresql.org/docs/current/functions-datetime.html#FUNCTIONS-DATETIME-DELAY

[fuyufjh]

LGTM

[BugenZhao]

LSTM!!!

[codecov]

Codecov Report

Merging #12294 (8dbf04a) into main (c07633a) will decrease coverage by 0.01%.
Report is 3 commits behind head on main.
The diff coverage is 70.58%.

@@            Coverage Diff             @@
##             main   #12294      +/-   ##
==========================================
- Coverage   69.97%   69.97%   -0.01%     
==========================================
  Files        1408     1409       +1     
  Lines      235155   235180      +25     
==========================================
+ Hits       164550   164563      +13     
- Misses      70605    70617      +12     

Flag	Coverage Δ
rust	69.97% <70.58%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
src/expr/src/vector_op/delay.rs	16.66% <16.66%> (ø)
src/expr/macro/src/gen.rs	97.02% <100.00%> (+<0.01%)	⬆️
src/expr/macro/src/lib.rs	91.39% <100.00%> (+0.09%)	⬆️
src/expr/macro/src/parse.rs	90.86% <100.00%> (+0.14%)	⬆️
src/expr/macro/src/types.rs	93.47% <100.00%> (+0.29%)	⬆️
src/expr/src/vector_op/proctime.rs	100.00% <100.00%> (ø)
src/frontend/src/binder/expr/function.rs	78.84% <100.00%> (+0.07%)	⬆️
src/frontend/src/expr/pure.rs	87.69% <100.00%> (ø)

... and 2 files with indirect coverage changes

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