modified existing extrema algo tests

[sleepingeight]

Fixes #6627

Proposed Changes

• Added a new test utility random_repeat to generate vectors having repeated values.
• This utility is used to test the extrema algorithms, and I've verified that the existing implementations work properly.

Any background context you want to provide?

Used uniform_int_distribution to generate random numbers.
Tests for container_algorithms can also be modified, but the tests need to be modified to not use sentinel (as we have duplicate values in our vector). I can update the tests if usage of sentinel can be removed in these tests.

Checklist

Not all points below apply to all pull requests.

• I have added a new feature and have added tests to go along with it.
• I have fixed a bug and have added a regression test.
• I have added a test using random numbers; I have made sure it uses a seed, and that random numbers generated are valid inputs for the tests.

[StellarBot]

Can one of the admins verify this patch?

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.03%	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (dcf267d)	194034	165080	85.08%
Head commit (c88e3ec)	193847 (-187)	164979 (-101)	85.11% (+0.03%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6724)	36	36	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[hkaiser]

LGTM, thanks!

[hkaiser]

• This utility is used to test the extrema algorithms, and I've verified that the existing implementations work properly.

I wouldn't like removing the tests realted to sentinels.