Fix NVL domain tag collision in CtranTestBootstrap by creating isolated bootstrap for nvl domain

[Regina8023]

Summary:
D98025086 introduced CtranTestBootstrap which implements NVL domain
operations (allGatherNvlDomain, barrierNvlDomain) via pairwise send/recv
with auto-incrementing tags starting from tag=0.

During ctranInit(), CtranAlgo::SharedResource calls these NVL domain
operations, which write data to TcpStoreBootstrap under a fixed key
keyed by (sender, receiver, tag). Later, test code calling
bootstrap_->send()/recv() with tag=0 directly (e.g. sockSend/sockRecv
in CtranIbDistUT) collides with these NVL domain keys.

Since TcpStoreBootstrap::recv does store_->wait(key) followed by
store_->get(key), and the key already exists from the NVL domain
operation, wait() returns immediately with stale NVL data (wrong size),
causing a data size mismatch and test failure.

Fix: add IBootstrap::duplicate() — a virtual method that each bootstrap type implements to create a new instance with isolated send/recv namespace:

• TcpStoreBootstrap: wraps the underlying store in c10d::PrefixStore so all keys are prefixed and never collide with the original bootstrap.
• MpiBootstrap: duplicates the communicator via MPI_Comm_dup so tags on the new communicator are independent.
• Default: returns nullptr (callers must override).

CtranTestBootstrap calls duplicate() in its constructor and asserts the result is non-null. NVL-domain operations use the isolated bootstrap for pairwise send/recv, while global operations (allGather, barrier, send, recv, broadcast) delegate to the primary bootstrap. No tag restrictions remain.

New tests added:

• DirectSendRecvAndNvlDomainWithSameTagAreIndependent: NVL-domain allGather followed by direct send/recv with tag=0 — confirms no collision.
• InterleavedDirectSendRecvAndNvlDomainAreIndependent: 3 rounds of interleaved direct send/recv and NVL-domain allGather, both using tag=0 — confirms repeated operations never interfere.

Reviewed By: minsii

Differential Revision: D98649856

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@Regina8023 has exported this pull request. If you are a Meta employee, you can view the originating Diff in D98649856.

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This pull request has been merged in 41b8b99.