feat(stellar): add streaming scan and fetch APIs

[xJeffx23]

Summary

• Adds scanAnnouncementsStream — async generator, O(window) memory, configurable window (default 64), clean cancellation via finally/iter.return()
• Adds fetchAnnouncementsStream — wraps paginated Soroban RPC, yields per-page, never accumulates full set
• fetchAnnouncements refactored as thin wrapper over streaming version
• scanAnnouncements marked @deprecated, points consumers to stream API

Usage

for await (const match of scanAnnouncementsStream(fetchAnnouncementsStream('stellar'), viewKey, spendPub, spendScalar)) {
  notify(match)
}

Tests

• 13 tests for scanAnnouncementsStream: match, filter, cancellation + source cleanup, window=1, window=200, memory benchmark
• 8 tests for fetchAnnouncementsStream: pagination, cursor, probe error, early return, URL override, cancellation
• Memory benchmark: 100k announcements < 10× memory of 1k ✅

Follow-up: Spectre connector migration

Spectre agents currently use the deprecated scanAnnouncements path. Once this PR merges, the connector must be updated:

// Before (deprecated — loads full array into memory)
const matches = await scanAnnouncements(await fetchAnnouncements('stellar'), v, K, m);

// After (streaming — O(window) memory, TEE-safe)
for await (const match of scanAnnouncementsStream(fetchAnnouncementsStream('stellar'), v, K, m, { window: 64 })) {
handleMatch(match);
}

At current announcement growth rate the deprecated path will OOM the TEE within ~6 months of mainnet. Migration must happen before launch.

Closes #9

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[truthixify]

The streaming scan + fetch generator API additions are what we want for issue #9. Rebase needed before merge, your branch is off pre-develop main so the current diff would undo work in #13/#14/#16.

git fetch origin
git rebase origin/develop
git push --force-with-lease

Keep the streaming additions in src/chains/stellar/scan.ts and your new tests; resolve conflicts by keeping develop's versions for files you didn't intend to change. Thanks @xJeffx23.

[truthixify]

The new commit (style: format stellar streaming test files with prettier) is just a formatting pass, but the rebase against develop didn't actually happen. Merge base is still f383081 which is before #13, #14, #16, and #37 all landed.

Could you do the actual rebase? Quick version:

git fetch origin
git rebase origin/develop
# resolve conflicts in src/chains/stellar/* by keeping develop's versions
# resolve in test/chains/stellar/announcements.test.ts by keeping develop's
# your streaming additions in src/chains/stellar/scan.ts and the new tests in scan.test.ts should layer in cleanly
git push --force-with-lease

After that the diff should only show your streaming additions, no reverts. Thanks @xJeffx23.

[xJeffx23]

Hi @truthixify ! Yes, absolutely.

I had an unexpected situation come up and had to step away before I could finish pushing the remaining commits, so the PR is currently incomplete.

Sorry for the delay. I'll push the updated commits in the next few minutes.