Add a (FIXED N) type for fixed-length byte arrays (#277)

* Add a (FIXED N) type for fixed-length byte arrays

`FixedType { int32 length }` in the `Type` oneof, written `(FIXED N)`. In CSV data a
value is 2N hex digits, most significant byte first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Update proto/relationalai/lqp/v1/logic.proto

Co-authored-by: Nikolas Göbel <nikolas.goebel@relational.ai>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Nikolas Göbel <nikolas.goebel@relational.ai>

Author: 3 people

meta/src/meta/grammar.y

@@ -147,6 +147,7 @@
 %nonterm false logic.Disjunction
 %nonterm ffi logic.FFI
 %nonterm ffi_args Sequence[logic.Abstraction]
+%nonterm fixed_type logic.FixedType
 %nonterm float_type logic.FloatType
 %nonterm float32_type logic.Float32Type
 %nonterm formula logic.Formula
@@ -579,6 +580,10 @@ type
       construct: $$ = logic.Type(uint32_type=$1)
       deconstruct if builtin.has_proto_field($$, 'uint32_type'):
         $1: logic.UInt32Type = $$.uint32_type
+    | fixed_type
+      construct: $$ = logic.Type(fixed_type=$1)
+      deconstruct if builtin.has_proto_field($$, 'fixed_type'):
+        $1: logic.FixedType = $$.fixed_type
 
 unspecified_type
     : "UNKNOWN"
@@ -635,6 +640,12 @@ decimal_type
         $3: Int64 = builtin.int32_to_int64($$.precision)
         $4: Int64 = builtin.int32_to_int64($$.scale)
 
+fixed_type
+    : "(" "FIXED" INT ")"
+      construct: $$ = logic.FixedType(length=builtin.int64_to_int32($3))
+      deconstruct:
+        $3: Int64 = builtin.int32_to_int64($$.length)
+
 boolean_type
     : "BOOLEAN"
       construct: $$ = logic.BooleanType()

proto/relationalai/lqp/v1/logic.proto

@@ -425,6 +425,7 @@ message Type {
     Int32Type int32_type = 12;
     Float32Type float32_type = 13;
     UInt32Type uint32_type = 14;
+    FixedType fixed_type = 15;
   }
 }
 
@@ -459,6 +460,11 @@ message Float32Type {}
 
 message UInt32Type {}
 
+// A fixed-length byte array of `length` bytes.
+message FixedType {
+  int32 length = 1;
+}
+
 message Value {
   oneof value {
     string string_value = 1;