feat: add default flag options

[RodrigoVillar]

Why this should be merged

As mentioned in #3996 (comment), test suites should ideally be able to set the default number of nodes for a test. Rather than extending the current RegisterFlagsWithDefaultX() pattern to support a default node count, this PR refactors setting the default flag values to use an options pattern.

How this works

Registering a flags default values is now done via RegisterFlagsWithOptions(). Calling this function without any arguments is equivalent to previously calling RegisterFlags.

How this was tested

CI

Need to be documented in RELEASES.md?

N/A

[Copilot]

Pull Request Overview

This PR refactors flag registration to use an options pattern for default values, allowing tests to specify a default node count (and owner) when registering flags.

• Introduces DefaultOptions and DefaultOption types with WithDefaultNodeCount/WithDefaultOwner helpers.
• Replaces RegisterFlags and RegisterFlagsWithDefaultOwner calls with RegisterFlagsWithOptions.
• Updates flag constructors to use the provided default node count.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/load2/main/main.go	Added defaultNodeCount constant and passed it via RegisterFlagsWithOptions
tests/load/c/main/main.go	Switched from RegisterFlags to RegisterFlagsWithOptions
tests/fixture/tmpnet/tmpnetctl/main.go	Supplied tmpnet.DefaultNodeCount into NewStartNetworkFlagSetVars
tests/fixture/tmpnet/flags/start_network.go	Extended constructors to accept defaultNodeCount and wire it through
tests/fixture/e2e/flags.go	Added options pattern, but RegisterFlagsWithDefaultOwner is misimplemented
tests/e2e/e2e_test.go	Updated to call RegisterFlagsWithOptions(e2e.WithDefaultOwner(...))
tests/antithesis/config.go	Replaced RegisterFlags() with RegisterFlagsWithOptions()

Comments suppressed due to low confidence (2)

tests/fixture/e2e/flags.go:162

• The RegisterFlagsWithDefaultOwner function is declared to return *FlagVars but currently returns an int. It should delegate to RegisterFlagsWithOptions, e.g.: return RegisterFlagsWithOptions(WithDefaultOwner(defaultOwner)).

}

tests/fixture/e2e/flags.go:155

• This return statement returns an int inside RegisterFlagsWithDefaultOwner, but the function signature expects *FlagVars. Update to return the result of RegisterFlagsWithOptions instead.

	return d.nodeCount

[maru-ava]

(No action required) I still think this a pretty complicated alternative to using a struct.

type Defaults struct {
  Owner     string
  NodeCount int
}
...
flags.RegisterFlags(flags.Defaults{})