fix Stagehand headless mode

[shrey150]

Why

Currently, the headless option for local browser launch is hardcoded to False by default, which doesn't allow for configuration through the Stagehand config.

What Changed

• Added a new headless configuration option to StagehandConfig with a default value of False
• Modified the local browser launch options to use the headless setting from the Stagehand config when not explicitly specified

Test Plan

• Verify that browsers launch in headless mode when the config option is set to True
• Verify that browsers launch in non-headless mode when the config option is set to False
• Confirm that explicitly setting headless in launch options still overrides the config value

[shrey150]

• Fix broken tests #237
• Bump litellm to 1.80.0 #234
• fix Stagehand headless mode #236 👈 (View in Graphite)
• main

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