[WebGPU] Batch streamless GPU-to-GPU copy vectors (#33567)
### Description
<!-- Describe your changes. -->
Batch compatible streamless GPU-to-GPU `OrtApi::CopyTensors` vectors
into one call-local recording and queue submission by default.
- Encode copies in array order, preserving dependencies between entries.
- Retain the context through submission and isolate recordings for
concurrent calls and error recovery.
- Preserve existing paths for single copies, CPU transfers, explicit
streams, and incompatible vectors.
- Add provider tests for submission counts, stream routing, copy
dependencies, error recovery, buffer lifetimes, and concurrent Session
teardown.
No public API/ABI changes or experimental flags are introduced.
### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Fixed-state caching can issue many small GPU copies during each
execution phase. Submitting every copy separately adds avoidable host
and queue-submission overhead. This change allows callers to submit
those copies together without adding a host-completion wait.
The companion consumer is microsoft/onnxruntime-genai#2775. Together,
the changes saved approximately 0.92 seconds for baseline generation and
1.52 seconds for DFlash2 width 3 in isolated A100 measurements with 512
generated tokens. These savings are configuration-dependent; generated
tokens, speculative counters, and final fixed-state bytes were
unchanged.
Validation: Release runtime/plugin builds passed. The expanded WebGPU
provider suites passed 66 tests, and serialized compatibility passed 24
tests, with no skips and two pre-existing disabled tests.
Formatting/lint checks passed. Local execution used Linux/Vulkan on an
A100; other backends remain for platform CI.
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
