feat(gslice): Add partial sort for gslice

[limits220284]

What

PartialSort sorts only the first k smallest elements of a slice in ascending order. The rest of the elements are left unordered.

• If k is 0 or less, nothing happens.
• If k is greater than or equal to the slice length, the whole slice is sorted.

Why

This is useful when you only need the smallest k elements in order, instead of sorting the entire slice. It’s more efficient for large datasets when you only care about the top results.

Motivation

Real World Example

• In a batch processing system, may want to select the next k shortest jobs to run, without needing to sort all pending jobs.

Aligns with similar patterns in other languages

• std::partial_sort in Cpp
• heapq.nsmallest in Python

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.79%. Comparing base (f5f07b9) to head (eee3c16).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #19   +/-   ##
=======================================
  Coverage   95.79%   95.79%           
=======================================
  Files          34       34           
  Lines        4443     4449    +6     
=======================================
+ Hits         4256     4262    +6     
  Misses        144      144           
  Partials       43       43           

Flag	Coverage Δ
go-1.18.x	94.92% <100.00%> (+<0.01%)	⬆️
go-1.19.x	94.65% <100.00%> (-0.27%)	⬇️
go-1.20.x	95.25% <100.00%> (-0.07%)	⬇️
go-1.21.x	95.25% <100.00%> (-0.40%)	⬇️
go-1.22.x	95.32% <100.00%> (+<0.01%)	⬆️
go-1.23.x	95.32% <100.00%> (+0.07%)	⬆️
go-1.24.x	95.25% <100.00%> (+0.07%)	⬆️
unittests	95.79% <100.00%> (+<0.01%)	⬆️

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[SilverRainZ]

Hello, thank you for your contribution! Can you please give some real-world cases in the description?

@XQ-Gang, I have been away from Go's code for a long time, and I don't know the current internal situation of ByteDance. I am not sure whether a function should be added (of course I will try to give suggestions). I think this decision should be made by you.

[limits220284]

Hello, thank you for your contribution! Can you please give some real-world cases in the description?

@XQ-Gang, I have been away from Go's code for a long time, and I don't know the current internal situation of ByteDance. I am not sure whether a function should be added (of course I will try to give suggestions). I think this decision should be made by you.

I have updated the description. If anything else is needed, please let me know.

[XQ-Gang]

Hello, thank you for your contribution! Can you please give some real-world cases in the description?
@XQ-Gang, I have been away from Go's code for a long time, and I don't know the current internal situation of ByteDance. I am not sure whether a function should be added (of course I will try to give suggestions). I think this decision should be made by you.

I have updated the description. If anything else is needed, please let me know.

@limits220284 有几个问题可以讨论

1. 如果想要获取topk元素，为什么不直接提供一个类似nlargest/nsmallest函数，而是使用partial_sort，还需要二次操作才能获取。
2. func PartialSort[T constraints.Ordered](s []T, k int) 的语法只能处理升序排序一种场景，不具备通用性，如果想要使用，建议多提供PartialSortBy有less函数输入，或者提供明确的取最大N个或者最小N个。