Migrate to math/rand/v2

[dbussink]

This moves all existing usage of math/rand to use math/rand/v2 instead. This is a new package available in Go 1.22 and later. See also:

https://tip.golang.org/doc/go1.22#math_rand_v2

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 62.71186% with 22 lines in your changes are missing coverage. Please review.

Project coverage is 65.69%. Comparing base (61db2db) to head (8e9195e).

Files	Patch %	Lines
go/vt/vttest/randomdata.go	0.00%	9 Missing ⚠️
go/vt/sqlparser/random_expr.go	75.00%	4 Missing ⚠️
...admin/cluster/discovery/fakediscovery/discovery.go	0.00%	2 Missing ⚠️
go/cmd/vtclient/cli/vtclient.go	0.00%	1 Missing ⚠️
...smartconnpool/benchmarking/legacy/resource_pool.go	0.00%	1 Missing ⚠️
go/sqltypes/testing.go	88.88%	1 Missing ⚠️
go/vt/throttler/demo/throttler_demo.go	0.00%	1 Missing ⚠️
go/vt/topo/zk2topo/zk_conn.go	0.00%	1 Missing ⚠️
...o/vt/vtadmin/cluster/discovery/discovery_consul.go	50.00%	1 Missing ⚠️
go/vt/vtgate/fakerpcvtgateconn/conn.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15513      +/-   ##
==========================================
- Coverage   65.69%   65.69%   -0.01%     
==========================================
  Files        1564     1563       -1     
  Lines      194588   194575      -13     
==========================================
- Hits       127832   127819      -13     
  Misses      66756    66756              

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