fix: Typing when explicitly setting sideEffect in RestEndpoint

[ntucker]

Motivation

When using sideEffect: false with method: 'POST' on a RestEndpoint (e.g., JSON-RPC or
POST-based search endpoints), the sideEffect type resolved to never instead of false.
This caused type information to be completely lost — both true and false were assignable
to sideEffect, and the type didn't persist through .extend() chains.

The docs already state that explicit sideEffect overrides method inference, but the types
didn't implement this correctly.

Solution

Replace Extract<O['sideEffect'], undefined | true> with Extract<O['sideEffect'], boolean | undefined> across all 6 locations in RestEndpointTypes.ts where the sideEffect type parameter is computed.

The original Extract<..., undefined | true> filtered out false because false is not in
undefined | true, causing Extract<false, undefined | true> = never. Widening to
boolean | undefined preserves all valid sideEffect values (false, true, undefined)
while still satisfying the M extends boolean | undefined constraint.

Additionally, RestExtendedEndpoint was missing a sideEffect priority check entirely — it
only checked method. Added the same sideEffect > method > inherited priority chain used
everywhere else.

---

Note

Low Risk
Type-only changes to RestEndpoint generics plus added TS tests; no runtime behavior changes, with the main risk being downstream compile-time type differences.

Overview
Ensures RestEndpoint type inference respects explicit sideEffect values (including false) over method-based inference, fixing cases where sideEffect: false with method: 'POST' previously collapsed to never (and could be lost through .extend()).

Adds TypeScript regression tests covering constructor/extend()/chained extend() scenarios, plus a patch changeset and a release-note entry documenting the fix.

^{Written by Cursor Bugbot for commit 592ba96. This will update automatically on new commits. Configure here.}

[changeset-bot]

🦋 Changeset detected

Latest commit: 592ba96

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@data-client/rest	Patch
test-bundlesize	Patch
coinbase-lite	Patch

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[github-actions]

Size Change: 0 B

Total Size: 79.8 kB

ℹ️ View Unchanged

Filename	Size
examples/test-bundlesize/dist/App.js	3.42 kB
examples/test-bundlesize/dist/polyfill.js	308 B
examples/test-bundlesize/dist/rdcClient.js	10.2 kB
examples/test-bundlesize/dist/rdcEndpoint.js	5.84 kB
examples/test-bundlesize/dist/react.js	59.4 kB
examples/test-bundlesize/dist/webpack-runtime.js	726 B

_{compressed-size-action}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.13%. Comparing base (9aa648d) to head (592ba96).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

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  Coverage   98.13%   98.13%           
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  Files         150      150           
  Lines        2736     2736           
  Branches      537      537           
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  Hits         2685     2685           
  Misses         11       11           
  Partials       40       40           

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