feat(core): add advanced commands and crypto

[mroczect]

• feat(codec): support tag signature encoding
• feat(branch): add list branches command
• feat(command): register new command modules
• feat(tag): add signing support for tags
• feat(domain): add signature field to tag
• feat(error): add Unsupported error variant
• feat(gc): implement garbage collection removal
• feat(lib): re-export crypto and reflog modules
• feat(merge): add merge strategy trait
• feat(storage): add all_hashes and remove methods
• feat(storage): add reflog and object removal
• feat(storage): extend ObjectStore with all_hashes and remove
• test(tag): update test for signer option
• feat(describe): add describe command
• feat(fsck): add fsck command
• feat(log): add log graph command
• feat(merge): add octopus merge command
• feat(rebase): add rebase command
• feat(show): add show command
• feat(tag): add verify tag command
• feat(crypto): add signer and verifier traits
• feat(merge): add MergeStrategy trait
• feat(reflog): add reflog store trait