clar: fix parsing of test suite prefixes

Since writing multiple objects may all already exist in a single
packfile, avoid freshening that packfile repeatedly in a tight loop.
Instead, only freshen pack files every 2 seconds.

When writing an object, we calculate its OID and see if it exists in the
object database.  If it does, we need to freshen the file that contains
it.

Enable https transport for custom TLS streams

When passing in a specific suite which should be executed by clar
via `-stest::suite`, we try to parse this string and then include
all tests contained in this suite. This also includes all tests
in sub-suites, e.g. 'test::suite::foo'.

In the case where multiple suites start with the same _string_,
for example 'test::foo' and 'test::foobar', we fail to
distinguish this correctly. When passing in `-stest::foobar`,
we wrongly determine that 'test::foo' is a prefix and try to
execute all of its matching functions. But as no function
will now match 'test::foobar', we simply execute nothing.

To fix this, we instead have to check if the prefix is an actual
suite prefix as opposed to a simple string prefix. We do so by by
inspecting if the first two characters trailing the prefix are
our suite delimiters '::', and only consider the filter as
matching in this case.

Add get user agent functionality.

Fixed bug while parsing INT64_MIN