feat(firestore): new generic pipeline expressions

[daniel-sanche]

WIP

New Expressions:

• offset
• nor
• coalesce
• switch_on
• parent
• array_filter
• array_transform
• storage_size
• reference_slice

[gemini-code-assist]

Code Review

This pull request introduces several new pipeline expressions to the Firestore library, including offset, coalesce, switch_on, parent, and a logical Nor operator, supported by new system and unit tests. The reviewer suggested refactoring the coalesce and switch_on methods for better conciseness and identified typos in the switch_on docstring and a unit test variable name.

[gemini-code-assist]

For improved readability and conciseness, you can construct the arguments list and return in a single statement.

return FunctionExpression(
    "coalesce",
    [self] + [Expression._cast_to_expr_or_convert_to_constant(x) for x in others],
)

[gemini-code-assist]

There's a small inconsistency in the docstring. The operation name is switch_on, but it's written as switchOn here. For consistency with the function name and implementation, it should be switch_on.

Suggested change

	An Expression representing the switchOn operation.
	An Expression representing the switch_on operation.

[gemini-code-assist]

Similar to coalesce, this can be simplified into a single return statement for better readability.

return FunctionExpression(
    "switch_on",
    [self, Expression._cast_to_expr_or_convert_to_constant(result)]
    + [Expression._cast_to_expr_or_convert_to_constant(x) for x in others],
)

[gemini-code-assist]

There's a typo in the variable name infix_istance. It should be infix_instance.

infix_instance = arg1.offset(arg2)
assert infix_instance == instance