Add --min-duration option

A test runner already has a --durations option to print durations.
However, this isn't entirely satisfactory.

When there are many tests, this produces output spam which makes it hard
to find the test failure output.  Nevertheless, it is helpful to be
informed of tests which are unusually slow.

Therefore, introduce a new option --min-duration that causes all
durations above a certain threshold to be printed.  This allows slow
tests to be visible without mentioning every test.

include/internal/catch_commandline.cpp

@@ -170,6 +170,9 @@ namespace Catch {
             | Opt( [&]( bool flag ) { config.showDurations = flag ? ShowDurations::Always : ShowDurations::Never; }, "yes|no" )
                 ["-d"]["--durations"]
                 ( "show test durations" )
+            | Opt( config.minDuration, "seconds" )
+                ["-D"]["--min-duration"]
+                ( "show test durations for tests taking at least the given number of seconds" )
             | Opt( loadTestNamesFromFile, "filename" )
                 ["-f"]["--input-file"]
                 ( "load test names to run from a file" )

include/internal/catch_config.cpp

@@ -64,6 +64,7 @@ namespace Catch {
     bool Config::warnAboutMissingAssertions() const    { return !!(m_data.warnings & WarnAbout::NoAssertions); }
     bool Config::warnAboutNoTests() const              { return !!(m_data.warnings & WarnAbout::NoTests); }
     ShowDurations::OrNot Config::showDurations() const { return m_data.showDurations; }
+    double Config::minDuration() const                 { return m_data.minDuration; }
     RunTests::InWhatOrder Config::runOrder() const     { return m_data.runOrder; }
     unsigned int Config::rngSeed() const               { return m_data.rngSeed; }
     UseColour::YesOrNo Config::useColour() const       { return m_data.useColour; }

include/internal/catch_config.hpp

@@ -52,6 +52,7 @@ namespace Catch {
         Verbosity verbosity = Verbosity::Normal;
         WarnAbout::What warnings = WarnAbout::Nothing;
         ShowDurations::OrNot showDurations = ShowDurations::DefaultForReporter;
+        double minDuration = -1;
         RunTests::InWhatOrder runOrder = RunTests::InDeclarationOrder;
         UseColour::YesOrNo useColour = UseColour::Auto;
         WaitForKeypress::When waitForKeypress = WaitForKeypress::Never;
@@ -103,6 +104,7 @@ namespace Catch {
         bool warnAboutMissingAssertions() const override;
         bool warnAboutNoTests() const override;
         ShowDurations::OrNot showDurations() const override;
+        double minDuration() const override;
         RunTests::InWhatOrder runOrder() const override;
         unsigned int rngSeed() const override;
         UseColour::YesOrNo useColour() const override;

include/internal/catch_interfaces_config.h

@@ -69,6 +69,7 @@ namespace Catch {
         virtual int abortAfter() const = 0;
         virtual bool showInvisibles() const = 0;
         virtual ShowDurations::OrNot showDurations() const = 0;
+        virtual double minDuration() const = 0;
         virtual TestSpec const& testSpec() const = 0;
         virtual bool hasTestFilters() const = 0;
         virtual std::vector<std::string> const& getTestsOrTags() const = 0;