0.18 round 3: make Disc::sweep + Disc::patch pub (was pub(crate))

Round 3 step 1: lift the visibility on the two flat rip-phase verbs
so consumers (autorip + freemkv CLI) can call them directly instead
of going through Disc::copy's multipass dispatcher. Also lift their
option/outcome types and re-export at crate root.

- fn sweep -> pub fn sweep (with rustdoc explaining its role)
- fn patch -> pub fn patch (ditto)
- pub(crate) struct SweepOptions -> pub struct SweepOptions
- pub(crate) struct PatchOpts -> pub struct PatchOptions (renamed
  for consistency — both are 'Options')
- pub(crate) struct PatchOutcome -> pub struct PatchOutcome
- libfreemkv::{SweepOptions, PatchOptions, PatchOutcome} re-exports
  at crate root.

Disc::copy still exists and still calls Disc::sweep / Disc::patch
through the now-private sweep_internal / patch_internal wrappers.
Migration of the two autorip callers + the freemkv CLI's
disc_to_iso to direct sweep/patch is a follow-up; once those land
Disc::copy + CopyOptions + CopyResult delete in the same commit.

See (internal)/memory/0_18_redesign.md and
0_18_round3_migration_audit.md.

Single contributor: MattJackson.

src/lib.rs

@@ -167,8 +167,8 @@ pub use decrypt::{DecryptKeys, decrypt_sectors};
 pub use disc::{
     AacsState, AudioChannels, AudioStream, Clip, Codec, ColorSpace, ContentFormat, DamageSeverity,
     Disc, DiscFormat, DiscId, DiscTitle, Extent, FrameRate, HdrFormat, KeySource, LabelPurpose,
-    LabelQualifier, Resolution, SampleRate, ScanOptions, Stream, SubtitleStream, VideoStream,
-    classify_damage,
+    LabelQualifier, PatchOptions, PatchOutcome, Resolution, SampleRate, ScanOptions, Stream,
+    SubtitleStream, SweepOptions, VideoStream, classify_damage,
 };
 
 // ─── Streams ────────────────────────────────────────────────────────────────