Detect the branch structure in a more robust way

[draftcode]

This should address the issue where the stack adopt command fails when
it's invoked at the trunk branch. (#363)

Based on the feedbacks, it seems that the commit traversal is way slower
than expected. Try to be a bit more conservative when to traverse the
commits.

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Current Aviator status

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Stack

1. 👉 Detect the branch structure in a more robust way #384 👈 (this pr)

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FlexReview Summary

Based on the code complexity and the author's expertise score, these are the suggested reviewers:

• @jainankit (current review load: 1)
• @alex-aviator (current review load: 1)

See the list of alternate reviewers in the detailed breakdown below.

Detailed Breakdown

Author’s expertise score for the modified files:

• cmd/av/stack_adopt.go (1.00)
• cmd/av/stack_tree.go (1.00)
• demos/stack_adopt/stack_adopt_no_root.mp4 (1.00)
• demos/stack_adopt/stack_adopt_no_root.tape (1.00)
• demos/stack_adopt/stack_adopt_with_stack_root.mp4 (1.00)
• docs/av-stack-adopt.1.md (1.00)
• e2e_tests/stack_adopt_test.go (1.00)
• internal/git/git.go (1.00)
• internal/reorder/plan.go (1.00)
• internal/treedetector/detector.go (1.00)
• internal/treedetector/util.go (1.00)

Files	Reviewers
cmd/av/stack_adopt.go †, cmd/av/stack_tree.go †, docs/av-stack-adopt.1.md †, internal/git/git.go †, internal/reorder/plan.go †, internal/treedetector/detector.go †, internal/treedetector/util.go †	@jainankit (score: 0.73, current review load: 1)
cmd/av/stack_adopt.go †, demos/stack_adopt/stack_adopt_no_root.mp4 †, demos/stack_adopt/stack_adopt_no_root.tape †, demos/stack_adopt/stack_adopt_with_stack_root.mp4 †, e2e_tests/stack_adopt_test.go †, internal/git/git.go †	@alex-aviator (score: 0.26, current review load: 1)

† Indicates that the file doesn't need an expert review. (?)

See full breakdown of the reviewers on the Aviator webapp.

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