Slot Improvements

[ZergLev]

Description

Refactored and added some features for existing Slots and a new type of slot - RegexpGroupSlot, which reuses one regex.search() call to save on execution time in specific cases like LLM, where the amount of get_value() calls is important. Also more minor changes like adding a new condition - SlotEqualsValue.

Changes relevant for the user:

• Added SlotEqualsValue condition to check that a slot is equal to some value.
• Added RegexpGroupSlot class. (e.g. (regexp=regexp, groups={"date": 1, "month": 2, "year": 3}) would yield ValueSlots with the respective numbers meaning the number of the group that was found with this regular expression) A better explanation can be found in the tutorials.
• Group slots: Disallowed slots being named the same as class variables like string_format or allow_partial_extraction. A special exception will be raised in such cases.
• GroupSlot now accepts string_format parameter, which makes it's ExtractedGroupSlot's __str__ representation formatted with extracted slot values being the keywords. (e.g. "{date}.{month}.{year}" is the value of a birthday group slot instead of "{'date': ..., 'month': ..., 'year': ...}") Almost the same as fill_template function in SlotManager class, except this doesn't catch exceptions. A better explanation will be provided in the tutorials.
• Renamed success_only to save_on_failure.

Changes in the codebase (or others):

• Added _flatten_group_slot method (for now a copy of flatten_llm_group_slot in LLM Slots PR), unpacks a GroupSlots nested Slots into a single dictionary.
• Restructured slots.py (to reduce file length) -- moved concrete slot implementations to standard_slots.py, base classes are in base_slots.py, SlotManager is in slot_manager.py
• Removed if TYPE_CHECKING in standard_slots.py to allow using FunctionSlot without importing Message first (no, rebuild it instead)
• Pass previous slot value to slot extraction function (Write in tutorial how this is already possible)

Checklist

• Production code changes done
• Tests added
• Check if I didn't update API reference anywhere
• Add the 2_regexpgroupslot_and_string_format.py tutorial
• I have performed a self-review of the changes

To Consider

• Adding tools that simplify inheriting group slot and overwriting its get_value method to group multiple subslot extraction requests into one
• Add a test for _flatten_group_slot(), there isn't one right now.
• Update API reference / tutorials / guides
• Update .ignore files, scripts (such as lint), distribution manifest (if files are added/deleted)
• Search for references to changed entities in the codebase