feat: add flushPromises and peekPromiseState then deprecate promiseState

[lambdalisue]

Close #37

Note that the behavior is different so we cannot simply compare the performance but if users don't need to wait internal microtask queue, peekPromiseState is approx. 3,000 times faster than promiseState

file:///Users/alisue/ogh/jsr-core/asyncutil/peek_promise_state_bench.ts
benchmark      time (avg)        iter/s             (min … max)       p75       p99      p995
--------------------------------------------------------------- -----------------------------

group peekPromiseState (fulfilled)
current        309.9 ns/iter   3,226,890.9 (293.85 ns … 421.18 ns) 307.97 ns 397.7 ns 421.18 ns

group peekPromiseState (rejected)
current       428.95 ns/iter   2,331,284.6 (420.77 ns … 526.07 ns) 427.32 ns 518.06 ns 526.07 ns

group peekPromiseState (pending)
current       257.49 ns/iter   3,883,658.2 (251.18 ns … 285.46 ns) 258.1 ns 275.92 ns 277.24 ns


file:///Users/alisue/ogh/jsr-core/asyncutil/promise_state_bench.ts
benchmark      time (avg)        iter/s             (min … max)       p75       p99      p995
--------------------------------------------------------------- -----------------------------

group promiseState (fulfilled)
current         1.24 ms/iter         804.3    (20.67 µs … 5.48 ms) 1.19 ms 3.39 ms 4.79 ms

group promiseState (rejected)
current         1.32 ms/iter         760.1    (14.42 µs … 10.1 ms) 1.22 ms 5 ms 6.19 ms

group promiseState (pending)
current         1.31 ms/iter         762.0    (23.12 µs … 8.24 ms) 1.22 ms 4.05 ms 6.34 ms

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.10%. Comparing base (5950811) to head (45c948e).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #38      +/-   ##
==========================================
+ Coverage   93.00%   93.10%   +0.10%     
==========================================
  Files          14       16       +2     
  Lines         400      406       +6     
  Branches       38       38              
==========================================
+ Hits          372      378       +6     
  Misses         28       28              

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