Delegate assertTrue/assertFalse/fail to AssertJ

[juherr]

Summary

Follow-up to #20 (stacked on it — base is port-assertj-delegation). Extends the AssertJ
delegation to the remaining behaviour-identical entry points:

• assertTrue / assertFalse → assertThat(condition).as(message).isTrue() / .isFalse()
• fail(message) and fail(message, cause) → org.assertj.core.api.Assertions.fail(...)

Because the OO Assertion / SoftAssert wrappers delegate to org.testng.Assert, soft
assertions now use AssertJ for these checks too — no change needed in Assertion/SoftAssert
themselves. Only the failure-message text changes; pass/fail behaviour is identical.

Test updates (message-format only)

The AssertJ messages differ from TestNG's (and are multi-line), so four message-sensitive tests
were updated — behaviour assertions are unchanged:

• AssertTest#testAssertTrueMessage / testAssertFalseMessage — regexps now match AssertJ output
  ([msg] \nExpecting value to be true but was false).
• AssertionTest#test2_fails — regexp updated to the [Raw test] … AssertJ form.
• SoftAssertTest#testAssertAllCount — no longer counts report lines (AssertJ messages span
  multiple lines); it now asserts the failed assertion's message is reported exactly once, which
  preserves the original "one failure → reported once" intent.

Notes

• fail is the shared failure sink for the (deliberately non-delegated) assertEquals / collection
  assertions. Delegating it routes those through AssertJ's AssertionFailedError (a subclass of
  AssertionError) — the message text is still TestNG's (built by format(...)), only the
  exception subtype changes. The full suite confirms no assertEquals/collection test regressed.
• assertEquals / assertNotEquals / collection / array / expectThrows remain on TestNG's own
  implementation (unchanged scope vs Back org.testng.Assert with AssertJ for behaviour-identical assertions #20).

Testing

• ./mvnw clean test → BUILD SUCCESS, Tests run: 181, Failures: 0, Errors: 0, Skipped: 1.

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