Minimize UtExecution number produced by fuzzing and collect coverage statistics

[Markoutte]

Description

The coverage statistic should be collected to improve fuzzing. To store the result of concrete execution a trie is used. For every coverage trace the total number of the same traces available to further analysis. Also, fuzzing now doesn't generate UtExecution with same coverage trace which increases a performance a bit, because fuzzing can generate a zillion combinations.

Type of Change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Automated Testing

org.utbot.framework.plugin.api.TrieTest

Checklist (remove irrelevant options):

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• New documentation is provided or existed one is altered
• No new warnings
• All tests pass locally with my changes

[sergeypospelov]

I suggest to add some comments to public API of Trie class, because for me some return values (e.g., from remove and get) are not obvious.

Also, I expect (maybe wrongly), that remove from the Trie removes only one entry of the same string, but the following test fails:

    @Test
    fun testSearchingAfterDeletion() {
        val trie = stringTrieOf("abc", "abc", "abcde")
        assertEquals(3, trie.toList().size)

        val removed1 = trie.remove("abc")
        assertNotNull(removed1)

        val find = trie.get("abc")
        assertNotNull(find)

        val removed2 = trie.remove("abc")
        assertNotNull(removed2)
    }