NilPy: bitwise operators + augmented assignment

Part of [[feature-nilpy-corpus-uforth]] milestone 1. uforth census: += 83, & 24, -= 20, | 10, ~ 2, << 2.

• Lexer: & | ^ ~ << >> -> tkAmp/tkPipe/tkXor/tkLogNot/tkShl/tkShr (token kinds shared with the C frontend; ~ reuses tkLogNot as a shape token, NilPy-side meaning is bitwise not). Augassign += -= *= //= %= &= |= ^= <<= >>= -> the tk*Eq family (//= maps tkSlashEq, integer division).
• Parser: Python precedence chain PyParseBitOr > BitXor > BitAnd > Shift > (shared ParseExpr atom, which owns comparison+arithmetic). Deviation guard: a tyBoolean operand adjacent to a bitwise op errors with "parenthesize" — Python puts comparisons LOOSER than bitwise, Pascal's shared layer binds them tighter, so the mixed case must be explicit rather than silently misparsed.
• Statements: x op= e and self.f op= e rewrite to lhs = lhs op e.

Gate

test-nilpy green (+ test_nilpy_operators.npy), self-host byte-identical, testmgr quick.