feat: add AbortSignal support to HttpClient for request cancellation

[OTimileyin]

Closes #53

Description:

Adds signal?: AbortSignal to HttpRequestOptions so callers can cancel in-flight SDK requests. The external signal composes with the existing timeout controller via a per-attempt listener — whichever fires first wins. External aborts throw ABORTED; timeouts continue to throw TIMEOUT. Already-aborted signals short-circuit before any fetch work.

Semver impact: minor

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Linked Issue:

Closes #53

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Type of Change:

• 🐛 Bug fix (patch)
• ✨ New feature / method (minor)
• 💥 Breaking change (major)
• 📝 Documentation / TypeDoc update
• 🔧 Chore / refactor
• 🧪 Tests only

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Changes Made:

• src/errors/errorCodes.ts — added ABORTED = 'ABORTED' to GuildPassErrorCode
• src/http/http.types.ts — added signal?: AbortSignal to HttpRequestOptions
• src/http/httpClient.ts — early-abort guard; per-attempt listennal to internal AbortController; ABORTED vs TIMEOUT distinctionin catch block; listener cleanup on all code paths
• tests/httpClient.test.ts — three new tests: already-aborted sietch, timeout-only (no signal)
• docs/sdk-guide.md — added Cancellation section with usage example

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Public API Changes:

// HttpRequestOptions — new optional field
signal?: AbortSignal;

// GuildPassErrorCode — new error code
ABORTED = 'ABORTED',

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Test Evidence:

Test Files 9 passed (9)
Tests 103 passed (103)
Start at 04:16:32
Duration 3.88s (transform 731ms, setup 0ms, collect 1.76s, terepare 5.21s)

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Build Evidence:

CJS ⚡️ Build success in 1511ms
ESM ⚡️ Build success in 1513ms
DTS ⚡️ Build success in 20807ms

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• I have read CONTRIBUTING.md
• This PR is linked to an open issue
• pnpm typecheck passes
• pnpm lint passes
• pnpm test:run passes — all tests green
• pnpm build succeeds — dist/ generated cleanly
• All new public methods/types have TypeDoc comments
• New behaviour is covered by at least one Vitest unit test
• No new runtime dependencies added without prior maintainer approval
• docs/ updated if public API changed
• examples/ updated if new usage patterns were added
• Backwards compatibility maintained (or breaking change clearly noted above)

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Additional Notes:

AbortSignal.any() was considered but requires Node 20.3+; this Sals are composed manually viaaddEventListener/removeEventListener. AbortSignal.any() can replace this once Node 18 reaches EOL.