feat(sim): rutster-sim crate skeleton + Scenario/ScenarioStep types (slice-4½ S1)

The critical-path foundation for the benchmark + simulation harness.
Scenario is a TOML-deserializable scripted-caller data type; ScenarioStep
covers speak_loud / speak_quiet / pause / await_reply / end. Determinism is
the point -- reproducible thresholds in CI (ADR-0010). All other sim
modules land as stubs here + fill in across S2-S7. Threshold consts
(BARGE_IN_KILL_TIME_P99_MS = 80.0, MOUTH_TO_EAR_P99_MS = 700.0,
TICK_LAG_MAX_MS = 10.0, TICK_OVERRUN_PCT_MAX = 1.0, SWEEP_CONCURRENCIES =
[1,10,50]) land now per the plan's S1 step 2 note (used by S5/S6/S7 wiring).

Adds toml = 0.8 to workspace.dependencies (the first consumer; spec §1.1
claim of pre-existing membership was inaccurate).

Task S1 of slice-4½ -- everything else depends on this landing.

Signed-off-by: Aaron D. Lee <himself@adlee.work>

Cargo.lock

@@ -374,7 +374,7 @@ checksum = "e6361d5c062261c78a176addb82d4c821ae42bed6089de0e12603cd25de2059c"
 dependencies = [
  "cfg-if",
  "crossbeam-utils",
- "hashbrown",
+ "hashbrown 0.14.5",
  "lock_api",
  "once_cell",
  "parking_lot_core",
@@ -485,6 +485,12 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "92773504d58c093f6de2459af4af33faa518c13451eb8f2b5698ed3d36e7c813"
 
+[[package]]
+name = "equivalent"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
+
 [[package]]
 name = "errno"
 version = "0.3.14"
@@ -630,6 +636,12 @@ version = "0.14.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
 
+[[package]]
+name = "hashbrown"
+version = "0.17.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ed5909b6e89a2db4456e54cd5f673791d7eca6732202bbf2a9cc504fe2f9b84a"
+
 [[package]]
 name = "http"
 version = "1.4.2"
@@ -720,6 +732,16 @@ dependencies = [
  "unicode-normalization",
 ]
 
+[[package]]
+name = "indexmap"
+version = "2.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d466e9454f08e4a911e14806c24e16fba1b4c121d1ea474396f396069cf949d9"
+dependencies = [
+ "equivalent",
+ "hashbrown 0.17.1",
+]
+
 [[package]]
 name = "inout"
 version = "0.1.4"
@@ -1243,6 +1265,20 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "rutster-sim"
+version = "0.0.0"
+dependencies = [
+ "rutster",
+ "rutster-media",
+ "serde",
+ "thiserror 1.0.69",
+ "tokio",
+ "toml",
+ "tracing",
+ "url",
+]
+
 [[package]]
 name = "rutster-spend"
 version = "0.0.0"
@@ -1374,6 +1410,15 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "serde_spanned"
+version = "0.6.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bf41e0cfaf7226dca15e8197172c295a782857fcb97fad1808a166870dee75a3"
+dependencies = [
+ "serde",
+]
+
 [[package]]
 name = "serde_urlencoded"
 version = "0.7.1"
@@ -1689,6 +1734,47 @@ dependencies = [
  "tungstenite",
 ]
 
+[[package]]
+name = "toml"
+version = "0.8.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc1beb996b9d83529a9e75c17a1686767d148d70663143c7854d8b4a09ced362"
+dependencies = [
+ "serde",
+ "serde_spanned",
+ "toml_datetime",
+ "toml_edit",
+]
+
+[[package]]
+name = "toml_datetime"
+version = "0.6.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22cddaf88f4fbc13c51aebbf5f8eceb5c7c5a9da2ac40a13519eb5b0a0e8f11c"
+dependencies = [
+ "serde",
+]
+
+[[package]]
+name = "toml_edit"
+version = "0.22.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41fe8c660ae4257887cf66394862d21dbca4a6ddd26f04a3560410406a2f819a"
+dependencies = [
+ "indexmap",
+ "serde",
+ "serde_spanned",
+ "toml_datetime",
+ "toml_write",
+ "winnow",
+]
+
+[[package]]
+name = "toml_write"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5d99f8c9a7727884afe522e9bd5edbfc91a3312b36a77b5fb8926e4c31a41801"
+
 [[package]]
 name = "tower"
 version = "0.5.3"
@@ -1945,6 +2031,15 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "winnow"
+version = "0.7.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "df79d97927682d2fd8adb29682d1140b343be4ac0f08fd68b7765d9c059d3945"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "wit-bindgen"
 version = "0.57.1"