Feat: keep up with ts version

[ningkaiqiang]

fix: wrong elapsed days
feat: add next state
feat: clamp params and s

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.55172% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.82%. Comparing base (f56e448) to head (3134333).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/FSRS/Algorithm/FSRSAlgorithm.swift	95.12%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   89.56%   89.82%   +0.26%     
==========================================
  Files          11       11              
  Lines        1054     1101      +47     
==========================================
+ Hits          944      989      +45     
- Misses        110      112       +2     

Flag	Coverage Δ
unittests	89.82% <96.55%> (+0.26%)	⬆️

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[ishiko732]

var w = defaultW

Swift arrays are value types or reference types? If they are reference types, will the operation var w = defaultW affect defaultW? There is currently a bug in ts-fsrs that will corrupt default_w.

[ningkaiqiang]

In Swift, this won't affect defaultW.

[ishiko732]

LGTM