docs: add PR description for dedupe of defindex asset amount extracti…

[Vivian-04]

PR #592
Summary

• The get_asset_amounts_per_shares first-element extraction is already deduplicated on main.
• Both buildDefindexWithdrawTx and fetchDefindexPosition already call the shared helper getDefindexAssetAmountPerShares, which owns the parsing logic (Array.isArray(...) && length > 0 ? toBigInt(v[0]) : <fallback>) in exactly one place in defindex.ts (lines 52-54).
• rate-sources.ts also imports the same helper, so the response parse lives in a single location repo-wide. This was folded in via 5aebacd.
• The issue's proposed firstAssetAmount(value): bigint (returning 0n on empty) was deliberately not implemented: getDefindexAssetAmountPerShares must keep returning bigint | null, since rate-sources.ts relies on null to signal an unavailable price (see rate-sources.ts lines 315/324). Collapsing the fallback into the helper as 0n would be a behavior change outside the SDK/DeFindex scope.

Acceptance criteria

• A single shared helper (getDefindexAssetAmountPerShares) already replaces both inline extractions.
• Existing defindex.test.ts coverage for both call sites passes unchanged (20/20).
• No behavior change to either function's return value.

Test plan

• pnpm test — all 9 workspace test tasks pass (incl. defindex.test.ts 20/20)
• pnpm typecheck — all 8 packages pass
• pnpm lint — passes
• pnpm format:check — noted: on this Windows machine it flags 187 files only because core.autocrlf=true converts LF→CRLF on checkout; CI runs on Linux with LF and passes. Not a code issue, no file changes.

Closes #592

[vercel]

@Vivian-04 is attempting to deploy a commit to the Collins' projects Team on Vercel.

A member of the Team first needs to authorize it.

[Vivian-04]

waiting...