Add support for local SAM 3 checkpoint

[giswqs]

Fix opengeos/geoai#447.

Allows setting environment SAM3_CHECKPOINT_PATH to use local SAM 3 for QGIS Plugin

[Copilot]

Pull request overview

This PR adds support for using a local SAM3 checkpoint file by introducing a new environment variable SAM3_CHECKPOINT_PATH. When set, this environment variable allows users (particularly QGIS Plugin users) to specify a local checkpoint path instead of downloading from HuggingFace, addressing issue #447.

• Added environment variable handling to read SAM3_CHECKPOINT_PATH and override the checkpoint path
• Added validation to ensure the specified checkpoint path exists before use
• Set load_from_HF to False when using local checkpoints

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[Copilot]

The environment variable is retrieved twice using os.environ.get("SAM3_CHECKPOINT_PATH"). Store the result in a variable on line 203 to avoid the redundant call on line 204.

Suggested change

	if os.environ.get("SAM3_CHECKPOINT_PATH") is not None:
	checkpoint_path = os.environ.get("SAM3_CHECKPOINT_PATH")
	env_checkpoint_path = os.environ.get("SAM3_CHECKPOINT_PATH")
	if env_checkpoint_path is not None:
	checkpoint_path = env_checkpoint_path

[Copilot]

Consider stripping whitespace from the environment variable value to handle cases where SAM3_CHECKPOINT_PATH might have leading or trailing whitespace. This would prevent unexpected errors when users accidentally include whitespace in their environment variable definition.

Suggested change

	if os.environ.get("SAM3_CHECKPOINT_PATH") is not None:
	checkpoint_path = os.environ.get("SAM3_CHECKPOINT_PATH")
	load_from_HF = False
	env_checkpoint = os.environ.get("SAM3_CHECKPOINT_PATH")
	if env_checkpoint is not None:
	env_checkpoint = env_checkpoint.strip()
	if env_checkpoint:
	checkpoint_path = env_checkpoint
	load_from_HF = False

[github-actions]

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