linker+runtime: code review cleanup of the seven gates

* Tighten the OAM-DMA gate: the `has_oam` flag now ORs
   `__sprite_cycle_used` in addition to `__oam_used`. A hypothetical
   program that calls `cycle_sprites` without ever drawing would
   otherwise compile to an NMI that advances \$07EF each frame but
   never actually runs the DMA the cycling is meant to perturb.
   The stronger gate keeps the two markers semantically coupled
   (cycling presupposes DMA) and adds a test that verifies the
   DMA trigger is emitted for a cycle-only program.

 * Drop the unused `NmiOptions::any_input()` helper. The only
   consumer (`gen_nmi`) reads the two flags inline and I never
   wired up a second caller.

 * Fix the cycle-count claim in `NmiOptions::has_p2_input` /
   `has_p1_input` docstrings: LDA abs + LSR A + ROL zp is 11
   cycles per port, ×8 loop iterations = ~88 cycles, not the "~30"
   I wrote in the original commit. Also notes the ~12-cycle strobe
   + scaffold overhead that disappears when both ports are unused.

No behavioural change — all 622 Rust tests and 33 emulator
goldens still pass unchanged.

https://claude.ai/code/session_016kM6P7PukktBDqTZexrrAN

src/runtime/mod.rs

@@ -388,29 +388,19 @@ pub struct NmiOptions {
     pub has_oam: bool,
     /// When false, drop the three instructions that shift `$4017`
     /// (JOY2) into `ZP_INPUT_P2` from the NMI's 8-iteration input
-    /// loop. Single-player programs save ~6 bytes of code and ~30
-    /// cycles per frame (a `LDA abs`, an `LSR A`, and a `ROL zp`
-    /// running 8 times).
+    /// loop. Single-player programs save ~6 bytes of code and ~88
+    /// cycles per frame (LDA abs + LSR A + ROL zp = 11 cycles × 8
+    /// iterations).
     pub has_p2_input: bool,
     /// When false, drop the three instructions that shift `$4016`
     /// (JOY1) into `ZP_INPUT_P1`. If both `has_p1_input` and
     /// `has_p2_input` are false the whole strobe-and-loop block
     /// disappears — programs that never touch `button.*` pay
-    /// zero cycles for input sampling.
+    /// zero cycles for input sampling (~100 cycles: the 88-cycle
+    /// body plus the ~12-cycle strobe and loop scaffold).
     pub has_p1_input: bool,
 }
 
-impl NmiOptions {
-    /// Whether the program reads any controller input — the
-    /// necessary condition for emitting the strobe write to
-    /// `$4016` and the 8-iteration shift loop. Skipped entirely
-    /// when both ports are unused.
-    #[must_use]
-    pub fn any_input(&self) -> bool {
-        self.has_p1_input || self.has_p2_input
-    }
-}
-
 #[must_use]
 pub fn gen_nmi(opts: NmiOptions) -> Vec<Instruction> {
     let NmiOptions {