minor: add __all__ to strategy __init__

[szepesisz]

Thank you for your work @toumorokoshi!

Just a little idea I had:
Instead of the recommended "magic-value-esque" way:

from deepmerge.merger import Merger

merger = Merger(
    type_strategies=[(list, 'override'), (dict, 'merge'), (set, 'union')],
    fallback_strategies=['override'],
    type_conflict_strategies=['override']
)

I would prefer explicitly referencing the merging functions:

from deepmerge.merger import Merger
from deepmerge.strategy import (
    ListStrategies,
    DictStrategies,
    SetStrategies,
    FallbackStrategies,
    TypeConflictStrategies
)

merger = Merger(
    type_strategies=[
        (list, ListStrategies.strategy_override), 
        (dict, DictStrategies.strategy_merge), 
        (set, SetStrategies.strategy_union)
    ],
    fallback_strategies=[
        FallbackStrategies.strategy_override
    ],
    type_conflict_strategies=[
        TypeConflictStrategies.strategy_override
    ]
)

This exact code does run currently, although the type checkers report errors:

"ListStrategies" is not exported from module "deepmerge.strategy"
     Import from "deepmerge.strategy.list" instead [reportPrivateImportUsage]

The suggested form would require a whole bunch of import lines.

Same applies to the merger.py source code:

"ListStrategies" is not exported from module "..strategy" [reportPrivateImportUsage]

Listing the classes in the __all__ variable solves this.

[toumorokoshi]

Great, thank you! Yes, makes a lot of sense, and the explicit approach does seem better.