feat(conflict): Add the Tango conflict analyzer

[manjari25]

Why

The orchestrator has no conflict analyzer that looks at the build graph, so batches touching different files but sharing affected targets run in parallel. The Tango analyzer compares the targets each batch affects, using the signatures, store, cache and request types from the earlier PRs in this stack.

What

• Analyze signs the batch being analyzed (cache, then store, then Tango, created once) and reports ConflictTypeTargetOverlap for each in-flight batch whose recorded signature shares a target ID.
• An in-flight batch is never sent to Tango. A missing record (ErrNoSignature) or a store error fails the analysis.
• SignatureCache is exported so one cache can be shared across queues. The base revision comes from Params.BaseRevision, a function returning a commit SHA.
• Not included: dictionary label writes and concurrent in-flight reads (marked TODO(tango)), the base-revision source, a real Tango adapter, and wiring. Nothing constructs the analyzer yet.

Test Plan

bazel test //submitqueue/extension/conflict/tango/...
CI

Issue