fix: isolate callId counter per sandbox for parallel test support

[singhvishalkr]

When tests run in parallel with separate sandboxes, the \calledImmediatelyBefore\ and \calledImmediatelyAfter\ assertions fail unexpectedly. This happens because proxy-invoke.js uses a global \callId\ counter shared across all sandboxes.

The fix introduces a per-sandbox context object that holds its own \callId\ counter. Each sandbox passes this context through the spy/stub/fake creation chain, and the proxy stores it for use during invocation.

Implementation:

• proxy-invoke.js: Use \ his.sinonContext.callId\ instead of a global variable, with a default context for backward compatibility when used outside sandboxes
• proxy.js: Accept optional context parameter and store it on the proxy
• spy.js/stub.js/fake.js: Thread context through creation functions
• sandbox.js: Create a sandbox-specific context and pass it to spy/stub/fake via new \withContext\ methods

Added tests that verify call order assertions work correctly across independent sandboxes.

The public API remains unchanged. Direct use of \sinon.spy()\ without a sandbox uses a shared default context (same behavior as before), while sandbox-created spies/stubs/fakes get isolated counters.

Fixes #2472

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