docs: clarify address-sync catch-up nonce and buffer comments

[QuantumExplorer]

Issue being fixed or feature implemented

Review follow-ups to #3650 (stacked on top of its branch). Comment-only — no behavior change, no logic touched. Addresses three reviewer notes:

1. The synthesized-nonce comment was misleading. It claimed clients recover via AddressInvalidNonceError.expected_nonce, but there is no such handler anywhere in rs-sdk / rs-platform-wallet / swift-sdk. The actual reason nonce = 0 is harmless is that every address-spend path re-fetches the authoritative nonce at build time (fetch_inputs_with_nonce + nonce_inc in address_inputs.rs), so the synced value is cosmetic and never lands in a broadcast transition. A future reader following the old comment would go hunting for a recovery path that doesn't exist.
2. result.absent.remove(...) was undocumented. It's a deliberate fix that keeps found and absent disjoint when a post-checkpoint funding lands on an address the branch scan proved absent (previously the address could appear in both sets). Now commented as such at both call sites.
3. In-source reviewer handle / PR number removed. The unbounded-buffer NOTE referenced @thepastaclaw and PR #3650, which go stale once merged into history. Kept the substance (bounded-memory mitigation: buffer keys only, re-derive on replay).

What was done?

• Rewrote the nonce comment in apply_block_changes to state the real reason the synthesized 0 is safe (build-time authoritative fetch), and downgraded the replay-site comment to a back-reference.
• Added comments documenting the found/absent disjointness fix at both the forward-pass and replay sites.
• Removed the reviewer handle and PR number from the buffer NOTE while preserving the mitigation guidance.

How Has This Been Tested?

No code paths changed — the diff is exclusively // line comments inside function bodies, so it cannot affect compilation or runtime behavior. The existing address_sync unit tests on the original PR remain the source of truth.

Breaking Changes

None.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

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[thepastaclaw]

✅ Review complete (commit 9b2f988)

[thepastaclaw]

Code Review

Comment-only PR clarifying three review notes in packages/rs-sdk/src/platform/address_sync/mod.rs from PR #3650. Both reviewers verified the new wording is factually accurate (e.g., fetch_inputs_with_nonce + nonce_inc flow exists, no AddressInvalidNonceError.expected_nonce handler), and there is no behavior change. Nothing to flag.