Add git replay update strategy

[Copilot]

Summary

Adds support for the experimental git replay command as a new replay update strategy when updating a stack.

Changes

New --replay flag

• Added --replay option to CommonOptions, wired into UpdateStackCommand and SyncStackCommand
• Strategy selection prompt now includes Replay alongside Merge and Rebase
• Specifying multiple strategies (--rebase, --merge, --replay) now raises a clear error

git replay support in GitClient

• IGitClient/GitClient gain ReplayFromSourceBranch(branchName, sourceBranchName, upstreamSha) and ReplayOntoNewParent(branchName, newParentBranchName, oldParentCommitSha) methods
• Each method runs git replay --onto <newbase> <upstream>..<branch> and then calls git update-ref with the output — no working directory changes required
• Conflict detection: checks stdout/stderr for CONFLICT markers; any non-zero exit throws ProcessException (or ConflictException on conflict)

Replay strategy in StackActions

• UpdateStackUsingReplay follows the same branch-line traversal and squash-merge re-parenting logic as the rebase strategy
• Since git replay doesn't touch the working directory, no branch switching is needed
• The upstream SHA for each replay is taken from the pre-operation branchStatuses snapshot, ensuring correct ranges even after parent branches have been updated
• Conflict handling: ConflictException is caught and re-thrown with a user-friendly message explaining that interactive resolution is not possible; users should resolve manually and retry with a different strategy

Tests

• UpdateStack_UsingReplay_WhenNoConflicts_CallsReplayForEachBranch — verifies ReplayFromSourceBranch is called for each branch with correct upstream SHAs and that no ChangeBranch calls are made
• UpdateStack_UsingReplay_WhenConflictDetected_ThrowsConflictException — verifies conflicts surface as exceptions
• UpdateStack_UsingReplay_WhenBranchHasMergedPullRequest_SkipsBranch — verifies inactive branches are skipped
• UpdateStack_UsingReplay_WhenBranchHasNoRemoteTrackingBranch_IsUpdated — verifies local-only branches are still replayed
• WhenReplayIsSpecified_StackIsUpdatedUsingReplay — command handler test
• WhenReplayAndRebaseAreSpecified_Throws — command handler test for mutual exclusion