[3/15] refactor(dag): extract query_stack_commits to Dag

[arxanas]

Stack:

• [1/15] feat(bisect): add guessing game example #1220
• [2/15] refactor(bisect): pass Bounds to Strategy::midpoint #1221
• [3/15] refactor(dag): extract query_stack_commits to Dag #1222
• [4/15] feat(git): export GitErrorCode from repo #1223
• [5/15] feat(submit): create SubmitStatus::Local #1224
• [6/15] feat(submit): make forges branch-agnostic #1225
• [7/15] feat(git): add Branch::rename method #1226
• [8/15] testing: configure repos cloned with Git::clone_repo_into #1227
• [9/15] refactor(dag): update some multi-parameter function argument names #1228
• [1/2] testing: forward RUST_LOG environment variable #1229
• [1/1] feat(submit:github): implement Github forge #1184
• [1/2] feat(smartlog): switch from ⊘ to ◌ for synthetic omitted-commit nodes #1230
• [13/15] wip: try to fix failing git-next tests #1231
• [1/2] testing(bisect): extract symbols into testing module #1232
• [15/15] wip: initial minimize #1233

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refactor(dag): extract query_stack_commits to Dag

So that we can use this logic in git-branchless-submit, which wants to be fundamentally aware of commit stacks as part of submitting.