Use context manager for PIL Image.open to ensure proper resource cleanup

[adamtheturtle]

Image.open() was used without explicit close or context manager. When the source is a file stream (e.g. multipart upload), this can hold file handles until garbage collection. Prefer 'with Image.open(...) as img:' to ensure files are closed promptly.

Fixes resource leak in:

• image_matchers.py (StructuralSimilarityMatcher)
• _query_validators/image_validators.py (validate_image_format, validate_image_dimensions, validate_image_is_image)
• _services_validators/image_validators.py (validate_image_integrity, validate_image_format, validate_image_color_space, validate_image_is_image)
• target.py (ImageTarget._post_processing_status)
• target_raters.py (_get_brisque_target_tracking_rating)

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Note

Low Risk
Mechanical resource-cleanup change (context managers around Image.open) with no functional logic changes expected beyond more deterministic file-handle release.

Overview
Ensures PIL.Image.open usages are wrapped in context managers across query validators, service validators, image matching, and target rating/status code paths so image/file handles are closed promptly.

This updates image dimension/format/is-image checks, integrity verification, SSIM matching, BRISQUE-based rating, and target post-processing status to use with Image.open(...) as ... (or as _) without changing validation thresholds or scoring logic.

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