Implement the AddImm opcode

It is a simple opcode. The hard part was finding a sqlite statement
that uses it =)

core/vdbe/execute.rs

@@ -6190,6 +6190,37 @@ pub fn op_shift_left(
     Ok(InsnFunctionStepResult::Step)
 }
 
+pub fn op_add_imm(
+    program: &Program,
+    state: &mut ProgramState,
+    insn: &Insn,
+    pager: &Rc<Pager>,
+    mv_store: Option<&Rc<MvStore>>,
+) -> Result<InsnFunctionStepResult> {
+    let Insn::AddImm { register, value } = insn else {
+        unreachable!("unexpected Insn {:?}", insn)
+    };
+
+    let current = &state.registers[*register];
+    let current_value = match current {
+        Register::Value(val) => val,
+        Register::Aggregate(_) => &Value::Null,
+        Register::Record(_) => &Value::Null,
+    };
+
+    let int_val = match current_value {
+        Value::Integer(i) => i + value,
+        Value::Float(f) => (*f as i64) + value,
+        Value::Text(s) => s.as_str().parse::<i64>().unwrap_or(0) + value,
+        Value::Blob(_) => *value, // BLOB becomes the added value
+        Value::Null => *value,    // NULL becomes the added value
+    };
+
+    state.registers[*register] = Register::Value(Value::Integer(int_val));
+    state.pc += 1;
+    Ok(InsnFunctionStepResult::Step)
+}
+
 pub fn op_variable(
     program: &Program,
     state: &mut ProgramState,

core/vdbe/explain.rs

@@ -1358,6 +1358,15 @@ pub fn insn_to_str(
                 0,
                 format!("r[{dest}]=r[{lhs}] << r[{rhs}]"),
             ),
+            Insn::AddImm { register, value } => (
+                "AddImm",
+                *register as i32,
+                *value as i32,
+                0,
+                Value::build_text(""),
+                0,
+                format!("r[{register}]=r[{register}]+{value}"),
+            ),
             Insn::Variable { index, dest } => (
                 "Variable",
                 usize::from(*index) as i32,

core/vdbe/insn.rs

@@ -877,6 +877,14 @@ pub enum Insn {
         dest: usize,
     },
 
+    /// Add immediate value to register and force integer conversion.
+    /// Add the constant P2 to the value in register P1. The result is always an integer.
+    /// To force any register to be an integer, just add 0.
+    AddImm {
+        register: usize, // P1: target register
+        value: i64,      // P2: immediate value to add
+    },
+
     /// Get parameter variable.
     Variable {
         index: NonZero<usize>,
@@ -1106,6 +1114,7 @@ impl Insn {
             Insn::ParseSchema { .. } => execute::op_parse_schema,
             Insn::ShiftRight { .. } => execute::op_shift_right,
             Insn::ShiftLeft { .. } => execute::op_shift_left,
+            Insn::AddImm { .. } => execute::op_add_imm,
             Insn::Variable { .. } => execute::op_variable,
             Insn::ZeroOrNull { .. } => execute::op_zero_or_null,
             Insn::Not { .. } => execute::op_not,