Replace abstract example tests with realistic greeting service scenario

[Copilot]

The example tests used meaningless placeholder names (theSystemSetup, somethingHappens, foofar/faff) that failed to demonstrate real BDD usage. This replaces them with a cohesive greeting service domain across all examples.

example_test.go

• All test functions renamed to TestGreetingService_* with descriptive suffixes
• Helper functions replaced: aRegisteredUserNamed, aGreetingIsRequested, withLocale, localeIsNotEnglish
• Skip example now uses a realistic condition (unsupported locale) instead of "fff"
• fmt and strings stdlib packages used naturally in implementation

func TestGreetingService_PersonalisesGreeting(t *testing.T) {
    gogiven.Given(t, aRegisteredUserNamed("Alice")).
        When(aGreetingIsRequested).
        Then(func(t base.TestingT, captured testdata.CapturedIO, givens testdata.InterestingGivens) {
            // the greeting should address the user by their registered name
            AssertThat(t, captured["greeting"], is.EqualTo("Hello, Alice!"))
        })
}

README.md

• All three code examples updated to match new function names
• New Example Four — Without a Given section added with anchor and code block
• Table of contents and HTML output anchor links updated

base/parsegiven_test.go

• All parser tests updated to reference new function names and correct expected output strings

[coveralls]

coverage: 63.793%. remained the same
when pulling d26af1b on copilot/update-example-tests-in-readme
into 9389ea5 on master.