perf: round 20 — iCal/vCard parse allocs, owned-DTO moves, Result-collect pre-size, NC etag/favorites emit

Benchmark-gated (benches/ROUND20.md), same rule as rounds 2-19: every change
ships with a BEFORE/AFTER counting-allocator micro-benchmark and a byte-value
equivalence gate; a non-winning AFTER is rolled back (never applied). The
rollback rule is encoded in the harness (GATE FAIL exit). All 8 sections pass.

Reproduce: cargo run --release --features bench --example bench_round20_micro

- A1 CalendarEvent iCal parse: replace the throwaway per-property
  HashMap<String,Vec<String>> (DTSTART/DTEND/RECURRENCE-ID) with a direct
  VALUE=DATE scan; prop_with_params kept #[cfg(test)] (6->2 allocs/event, 4.2x)
- A2 UserDto::from: add User::into_parts and MOVE image (<=512 KiB data URI)
  + ui_preferences JSON instead of cloning on every /api/auth/me (27->14 allocs)
- A3 parse_vcard: drop the per-line to_ascii_uppercase copy + the lines Vec;
  promote ascii_ci_contains to common::text and share it (8->1 allocs/contact)
- A4 Calendar/AddressBook DTO: into_parts move incl. custom_properties map (18->10)
- I1 file-listing repos: collect::<Result<Vec>>() size-hints to 0 and grows from
  capacity 0; pre-size with Vec::with_capacity (8->1 container reallocs, 4 sites)
- I4 plaintext_stream: lazy emit iterator instead of eager Vec collect (43x wall)
- C1 NC write_etag_element: borrowed pre-escaped quote events, no owned quoted
  String/escape re-alloc; byte-identical output (3->0 allocs/PROPFIND row)
- C3 NC favorites REPORT: map.remove() move instead of get().clone() (~7 allocs/fav)

Deferred (documented in ROUND20.md): NC oc:id/trashbin buffer reuse, I1 sibling
CardDAV/CalDAV listing paths, Contact JSONB Json<Vec<_>> decode, dedup
settle_batch &str bind, and a fast DoS-resistant hasher for hot trusted-key maps
(needs a dependency decision).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JsJjcVX9RoN96DMa35Wqzd

Cargo.toml

@@ -354,6 +354,22 @@ name = "bench_micro_allocs"
 path = "examples/bench_micro_allocs.rs"
 required-features = ["bench"]
 
+# Round-20 battery ────────────────────────────────────────────────────────────
+
+# Round-20 CPU/alloc micro-pack — CalendarEvent `prop_with_params` throwaway
+# HashMap → direct VALUE=DATE scan; `UserDto::from` clone-every-field → move
+# (image ≤512 KiB + ui_preferences JSON); `parse_vcard` per-line to_ascii_uppercase
+# + lines Vec → direct iterate + `common::text::ascii_ci_contains`; Calendar/
+# AddressBook DTO clone → move; listing `collect::<Result<Vec>>()` (size_hint 0)
+# → `Vec::with_capacity` + push; `plaintext_stream` eager Vec collect → lazy iter;
+# NC `write_etag_element` 3→0 allocs/row (borrowed pre-escaped quote events);
+# NC `oc:id` per-row String → reused buffer; favorites REPORT DTO clone → map move.
+# No Postgres.
+[[example]]
+name = "bench_round20_micro"
+path = "examples/bench_round20_micro.rs"
+required-features = ["bench"]
+
 # Round-19 battery ────────────────────────────────────────────────────────────
 
 # Round-19 CPU/alloc micro-pack — Basic-auth cache-key incremental blake3 (drop