feat(ur-sdk): allow migrating to eth position

[dianakocsis]

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Please title your PR according to the following types and scopes following conventional commits:

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Are there any breaking changes?

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[Ayoakala]

Left a couple comments for token mismatch invariants and validation

[snreynolds]

this change seems fine but I think the title of this PR is now misleading? we just now allow migrating weth -> eth but we don't specifically disallow weth positions on v4?

[graphite-app]

Graphite Automations

"Request reviewers once CI passes on sdks monorepo" took an action on this PR • (02/04/25)

2 reviewers were added and 1 assignee was added to this PR based on Siyu Jiang (See-You John)'s automation.