refactor!: simplify replay API — remove MatchStrategy, ReplaySource & Snapshots

[JosiahBull]

Summary

Two related simplifications of the replay/storage public API (bumps 0.4.0 → 0.5.0, one minor bump covering both breaking changes).

1. Remove MatchStrategy (commit bc0d76f)

The Custom matcher was never needed — replay only ever uses MethodUriAndBodyHash. Matching is now fixed to a single key: (method, origin-form URI [path + query], SHA-256 of body).

• Removed the MatchStrategy enum and CustomMatcher type alias.
• Dropped the strategy parameter from the replay constructors.
• lookup() collapses to the single hash-indexed path (no per-call match, no linear-scan branch).

2. Remove ReplaySource / Snapshots from the public API (commit 729f34b)

Replay is now configured purely by attaching a SnapshotStorage backend to an upstream — no caller-facing replay type.

• ReplaySource is now pub(crate), built internally from the backend's load() stream at run(); Snapshots is deleted.
• add_upstream_with / add_upstream_with_mode take Option<SharedStorage> directly.
• Added InMemoryStorage — a real in-memory SnapshotStorage in partly-proxy-types (promotes the former storage.rs doc example) — for filesystem-free replay/fixtures, replacing Snapshots::in_memory.
• Dropped the now-unused ReplaySource::from_jsonl.

Migration

// before
let replay = ReplaySource::from_jsonl(path, MatchStrategy::MethodUriAndBodyHash)?;
.add_upstream_with("api", cfg, mw, Some(Snapshots::from_storage(store, strategy)))

// after — construct a backend, attach it
let store: SharedStorage = Arc::new(JsonlStorage::open(path).await?);
.add_upstream_with("api", cfg, mw, Some(store))

// replay-only fixture (was Snapshots::in_memory)
let store: SharedStorage = Arc::new(InMemoryStorage::from(exchanges));
.add_upstream_with("api", cfg, mw, Some(store))

Versioning

0.5.0. Both commits are breaking; under the repo's pre-1.0 rule (minor = breaking boundary) one minor bump from main's 0.4.0 covers them and clears the cargo semver-checks gate (baseline = PR base = main).

Docs

SPECIFICATION.md §2/§3.3/§4/§4.1/§5/§8/§8.1/§8.1.1/§9.1/§20.1 rewritten for the fixed match key and the storage-backend attach model (also cleared leftover strategy args from the §4/§20.1 examples).

Testing

• cargo build --workspace --all-targets — clean
• cargo test --workspace — all 23 test binaries pass
• cargo clippy --workspace --all-targets — clean
• cargo fmt --check --all — clean