Rename "delay" buffer functions to "history" buffers.

The functions and associated tests related to managing time-stamped data buffers have been renamed from `mju_delay*` to `mju_history*` to better reflect their general purpose beyond just handling delays.

PiperOrigin-RevId: 866978339
Change-Id: I8655e91bce783287ad2adc412d13a1c39aa2c322

src/engine/engine_util_misc.h

@@ -89,7 +89,7 @@ MJAPI size_t mju_isValidBase64(const char* s);
 // returns number of bytes decoded (upper limit of 3 * (strlen(s) / 4))
 MJAPI size_t mju_decodeBase64(uint8_t* buf, const char* s);
 
-//------------------------------ delay buffers -----------------------------------------------------
+//------------------------------ history buffers ---------------------------------------------------
 
 // buffer layout: [user(1), cursor(1), times(n), values(n*dim)]
 // - user: 1 mjtNum reserved for user data (ignored by these functions)
@@ -98,20 +98,20 @@ MJAPI size_t mju_decodeBase64(uint8_t* buf, const char* s);
 // - values: n*dim values, contiguous at buf[n+2..n+2+n*dim-1]
 // total buffer size: 2 + n*(1 + dim)
 
-// initialize delay buffer with given times and values; times must be strictly increasing
+// initialize history buffer with given times and values; times must be strictly increasing
 // values is size n x dim
-MJAPI void mju_delayInit(mjtNum* buf, int n, int dim, const mjtNum* times,
-                         const mjtNum* values, mjtNum user);
+MJAPI void mju_historyInit(mjtNum* buf, int n, int dim, const mjtNum* times,
+                           const mjtNum* values, mjtNum user);
 
 // find insertion slot for sample at time t, maintaining sorted order
 // returns pointer to value slot (size dim) where caller should write
-MJAPI mjtNum* mju_delayInsert(mjtNum* buf, int n, int dim, mjtNum t);
+MJAPI mjtNum* mju_historyInsert(mjtNum* buf, int n, int dim, mjtNum t);
 
 // read vector value at time t; interp: 0=zero-order-hold, 1=linear, 2=cubic spline
 // returns pointer to sample in buffer on exact match (res untouched)
 // returns NULL and writes interpolated result to res otherwise
-MJAPI const mjtNum* mju_delayRead(const mjtNum* buf, int n, int dim,
-                                  mjtNum* res, mjtNum t, int interp);
+MJAPI const mjtNum* mju_historyRead(const mjtNum* buf, int n, int dim,
+                                    mjtNum* res, mjtNum t, int interp);
 
 //------------------------------ miscellaneous -----------------------------------------------------