Add unified MaskBuilder class replacing mixin-based factory pattern

[Copilot]

The mask builder system required composing 12+ mixin classes via MaskBuilderFactory to get a usable builder — opaque, fragile, and hard to type correctly.

Changes

• New MaskBuilder class (mask_builders/builder.py): Single concrete class with explicit, typed init arguments. No mixins, no factory. Implements all pipeline stages (storage allocation, coordinate scaling, scalar expansion, edge clipping, aggregation) directly.

  • storage: Literal["memmap", "in-memory"]
  • aggregation: Literal["mean", "max"]
  • auto_scale: bool — auto-computes mask extents and scales coordinates from source to mask space
  • expand_scalars: bool — GCD-compressed per-tile scalar expansion
  • StorageType and AggregationType type aliases exported for annotations

• __init__.py: Exports MaskBuilder, StorageType, AggregationType alongside existing symbols (fully backward-compatible; all mixin classes and MaskBuilderFactory preserved).

Usage

from ratiopath.masks.mask_builders import MaskBuilder

builder = MaskBuilder(
    storage="memmap",       # "memmap" | "in-memory"
    aggregation="mean",     # "mean" | "max"
    auto_scale=True,
    source_extents=source_extents,
    source_tile_extents=tile_extents,
    source_tile_strides=tile_strides,
    mask_tile_extents=tile_extents,
    channels=3,
    px_to_clip=2,
    dtype=np.float32,
)

builder.update_batch(data_batch, coords_batch)
assembled, overlap = builder.finalize()

Original prompt

Simplify the mask builders. Do not use mixins but instead use proper init arguments and classes. The output should be a single MaskBuilder class with arguments such as storage="mammap" | "in-memory". Everything should be properly typed.

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