WIP: alternative/follow-up to #5739 — flatten embedded interface method sets

[ltzmaxwell]

Status: WIP / draft. Alternative to, and follow-up on, #5739. Stacked on fix/alias_2; until that merges this PR's diff also shows #5739's commits — the net-new change here is the single commit fix(gnovm): flatten embedded interface method sets for type identity.

#5739 makes embedded struct alias names take the written spelling (correct), and ships a minimal interface fix that only re-equalizes an embedded alias with its target (interface{ SAlias } == interface{ Stringer }). This PR replaces that minimal interface fix with the deeper one.

• Flattens embedded interfaces into their method set at construction (doOpInterfaceType, staticTypeFromAST), so the embedded-interface name leaves the TypeID entirely. Interface identity becomes the flattened method set, matching Go.
• Fixes a divergence that exists on master independent of fix(gnovm): embedded type identity — struct field name + interface method-set flatten #5739: interface{ Stringer } == interface{ Str() string } (and embed-of-two vs methods-listed, diamond dedup) — not just the alias case.
• Keeps the runtime embedded-interface handling in FindEmbeddedFieldType/VerifyImplementedBy for already-persisted (pre-upgrade) state, whose Methods are still unflattened.
• Same-name/different-signature conflicts are rejected by go/types before the VM builds the type, so the dedup panic is should-not-happen (consistent with existing construction-time guards).
• Tests: iface_embed_id.gno (embed-vs-explicit, alias-vs-target, diamond); alias5.gno retained.

Consensus-breaking, distinct from #5739's struct break: anonymous-interface TypeIDs that embed other interfaces change. Must land with a chain upgrade.

Verified: Files -short, sdk/vm -run Gas, integration -run TestTestdata all green.

[Gno2D2]

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[ltzmaxwell]

Folded into #5739 — the flattening commit is now stacked there, so this standalone follow-up is redundant. Closing.