feat: avm unconstrained external call (#6846)

---------

Co-authored-by: Maddiaa0 <47148561+Maddiaa0@users.noreply.github.com>

barretenberg/cpp/pil/avm/avm_main.pil

@@ -116,6 +116,7 @@ namespace avm_main(256);
     pol commit sel_internal_return;
     pol commit sel_jump;
     pol commit sel_jumpi;
+    pol commit sel_external_call;
 
     // Halt program execution
     pol commit sel_halt;
@@ -276,6 +277,7 @@ namespace avm_main(256);
     sel_jump * (1 - sel_jump) = 0;
     sel_jumpi * (1 - sel_jumpi) = 0;
     sel_halt * (1 - sel_halt) = 0;
+    sel_external_call * (1 - sel_external_call) = 0;
 
     // Might be removed if derived from opcode based on a lookup of constants
     sel_mov * ( 1 - sel_mov) = 0;
@@ -413,7 +415,7 @@ namespace avm_main(256);
 
     //===== CONTROL_FLOW_CONSISTENCY ============================================
     pol INTERNAL_CALL_STACK_SELECTORS = (first + sel_internal_call + sel_internal_return + sel_halt);
-    pol ALL_CTRL_FLOW_SEL = sel_jump + sel_jumpi + sel_internal_call + sel_internal_return;
+    pol ALL_CTRL_FLOW_SEL = sel_jump + sel_jumpi + sel_internal_call + sel_internal_return + sel_external_call;
 
     pol ALL_BINARY_SEL = sel_op_and + sel_op_or + sel_op_xor;
     pol ALL_GADGET_SEL = sel_op_radix_le + sel_op_sha256 + sel_op_poseidon2 + sel_op_keccak + sel_op_pedersen;

barretenberg/cpp/pil/avm/constants.pil

@@ -30,3 +30,14 @@ namespace constants(256);
     // Other AVM specific constants
     pol INTERNAL_CALL_SPACE_ID = 255;
 
+    // Lengths of kernel output vectors
+    // Read requests
+    pol MAX_NULLIFIER_READ_REQUESTS_PER_CALL = 32;
+    pol MAX_NOTE_HASH_READ_REQUESTS_PER_CALL = 32;
+    pol MAX_PUBLIC_DATA_UPDATE_REQUESTS_PER_CALL = 32;
+    pol MAX_PUBLIC_DATA_READS_PER_CALL = 16;
+
+    // Emitting Data
+    pol MAX_NEW_NOTE_HASHES_PER_CALL = 16;
+    pol MAX_NEW_NULLIIFIERS_PER_CALL = 16;
+    pol MAX_NEW_L2_TO_L1_MSGS_PER_CALL = 2;