fix: migrate EPAlias to EPName where possible (#646)

[xieofxie]

Summary

Addresses #646 (migrate EPAlias to EPName where possible). EPNameOrAlias is the public-facing input type; EPName is the internal canonical form. This PR removes places where a bare alias was used where a canonical name belongs, and stops comparing against single alias literals.

Changes

• analyze/utils/ep_utils.py — infer_ihv_from_ep_name now does a direct, exact dict[EPName, IHVType] lookup covering every member of the EPName Literal. An unknown name now raises ValueError instead of silently defaulting to IHVType.MICROSOFT (the callers that matter already handle it: InformationEngine catches ValueError and falls back to loading all rules; the model validator catches it defensively). Also fixes a latent miss where CUDAExecutionProvider resolved to MICROSOFT instead of NVIDIA.
• serve/schema.py — EpSwitchRequest.ep was the only ep field still typed bare EPAlias; every sibling is EPNameOrAlias and manager.switch_ep already accepts EPNameOrAlias. Widened it for consistency so it accepts both "qnn" and "QNNExecutionProvider".
• compiler/utils.py — needs_format_conversion compared ep == "qnn", a single alias literal. An EP can have multiple aliases (e.g. nv_tensorrt_rtx / nvtensorrtrtx), and the canonical name itself wouldn't match. Now normalizes via normalize_ep_name and compares against the canonical "QNNExecutionProvider"; parameter widened to EPNameOrAlias.

Notes

• The compiler's EPConfig.provider deliberately remains alias-typed: every value it holds is an alias (provider="qnn", etc.), so retyping to EPName would require a value migration with serialization back-compat — out of scope here.
• An audit of all ~90 EPNameOrAlias call sites confirmed every one either normalizes before a canonical sink or forwards to a callee that does — no other un-normalized canonical-sink usages were found.

Tests

• Replaced the per-EP infer_ihv unit tests with one that verifies every EP_NAMES member resolves to an IHVType (enforcing map/Literal parity) plus an unknown-raises test.
• Updated fixtures that relied on the old lenient behavior to use canonical EP names (ACEExecutionProvider → VitisAIExecutionProvider; alias "openvino" → "OpenVINOExecutionProvider" in the validator tests).
• Added test_qlinear_for_qnn_canonical_name covering the canonical-name case that previously failed in needs_format_conversion.