fix(codegen): declare loop-local drawing-object handles (line/label/box)

[luisleo526]

Problem

A variable assigned from a skipped visual call (line.new / label.new / box.new / …) was declared only when the namespace was table (SKIP_VAR_TYPES). For the other drawing namespaces the declaration was dropped. In script/if scope the var is a class member (declared anyway), but as a for-loop local it became undeclared:

var aoLines = array.new<line>()
for k = 1 to aoCount
    ln = line.new(...)        // dropped
    array.push(aoLines, ln)   // -> aoLines.push_back(ln);  // no `ln`

error: use of undeclared identifier 'ln'

Found running real-world strategies through the engine — common in webhook/DCA bots that draw AO level lines in a loop (11 strategies in the test set hit this).

Fix

Always emit a default-valued local declaration for skip-expr assignments. The value is inert (drawing ops have no backtest effect) but references must compile. Removes the now-unused SKIP_VAR_TYPES import.

Tests / regression

• New tests/test_codegen_drawing_handles.py (line + label handles in a loop).
• No corpus regression: all 258 corpus probes transpile byte-identically with vs without this change (no corpus probe uses this pattern).
• End-to-end: a real strategy with this pattern compiles with 0 errors when combined with fix(codegen): escape C++ string literals (quotes/backslash/newline) #23 (string escaping).

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