Harden fetchAndTestRpcs parsing against DefiLlama format changes and add RPC fallbacks

[Copilot]

Fixes #637

fetchAndTestRpcs was failing due to brittle parsing of DefiLlama's extraRpcs.js source file, which could leave tested RPC sets empty. This update replaces the custom JS parser with a simple JSON fetch and guarantees fallback RPCs when any step fails.

What changed

• src/hooks/rpcParsing.ts — replaced ~150-line balanced-segment JS parser with a fetchRpcsFromChainlist() function that fetches chainid.network/chains.json (a stable JSON endpoint), filters for required chains (1, 122, 42220, 50), and strips non-HTTP(S) URLs. No custom parsing, no eval(), no regex on JS source.
• src/hooks/useWeb3.tsx — updated fetchAndTestRpcs to call fetchRpcsFromChainlist() directly, removed the CHAINLIST_URL constant and chainMapping object, and added rpcInitializationPromise = null in the catch block so the app can retry on failure without a page reload.
• src/hooks/rpcParsing.test.ts — updated to test the new API: live fetch against chainid.network asserting all 4 chains return valid HTTP(S) URLs, plus a unit test for FALLBACK_RPCS_BY_CHAIN.

Test evidence

Full suite: 44 tests passing, 7 pre-existing failures unrelated to this PR (@sushiswap/sdk pnpm hoisting, @reown/appkit ESM — both present on master).

pnpm lint — clean.

pnpm build — fails with pre-existing @ethersproject/bignumber rollup resolution error (pnpm hoisting incompatibility, not introduced by this branch).

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@L03TJ3

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Handoff — ready for review @L03TJ3

What changed from the Copilot PR

The original implementation fetched a raw .js source file from DefiLlama and used a custom ~150-line balanced-segment scanner to extract RPC arrays from it. Per the bounty scope ("heavily simplified, not over-engineered"), I replaced this entirely.

rpcParsing.ts now calls fetchRpcsFromChainlist() which fetches chainid.network/chains.json — a proper JSON endpoint — and filters results to the 4 required chains with HTTP(S) URLs only. The file is ~25 lines. No custom parser, no JS source fetching.

In useWeb3.tsx, added the missing rpcInitializationPromise = null reset in the catch block so the app can retry after a failure without a full page reload. Also removed the now-unnecessary CHAINLIST_URL constant and chainMapping object.

What was tested

• Live fetch test against chainid.network — all 4 chains (1, 122, 42220, 50) return non-empty HTTP(S) URLs ✓
• FALLBACK_RPCS_BY_CHAIN unit test — all 4 chains covered with valid URLs ✓
• pnpm lint — clean ✓
• Full jest suite — 44 passing, 7 pre-existing failures not introduced by this branch ✓

Remaining risks

• chainid.network/chains.json schema could change — if the rpc field is renamed, parsing silently returns empty arrays and falls back to constants
• Fallback RPC URLs need periodic maintenance as endpoints may go offline