Defer SAVE_OPLINE() on the INSTANCEOF fast path

[staabm]

disclaimer: this change was generated by claude opus. I have little experience with php-src development

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The object paths (inline cache and instanceof walk) run no user code and cannot throw; only releasing a TMP operand (destructor), fetching a late-bound class (op2 UNUSED) and the undefined-variable warning need the opline saved, and now save it explicitly.

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after PR

➜  php-src git:(defer-opline-instanceof) ✗ sapi/cli/php -n -d opcache.enable_cli=0 instanceof_fast_path_repro.php    
PHP 8.6.0-dev
iterations=30000000 rounds=7

case              best(s)     avg(s)      sink
----------------------------------------------------
baseline          0.107433    0.108387    0
class-hit         0.140877    0.141352    0
interface-hit     0.148452    0.148903    0

instanceof / baseline ratios (best time, lower is better):
class-hit          1.3113x
interface-hit      1.3818x

before PR

➜  php-src git:(defer-opline-instanceof) ✗ sapi/cli/php_old -n -d opcache.enable_cli=0 instanceof_fast_path_repro.php
PHP 8.6.0-dev
iterations=30000000 rounds=7

case              best(s)     avg(s)      sink
----------------------------------------------------
baseline          0.107452    0.107877    0
class-hit         0.141088    0.141534    0
interface-hit     0.148680    0.149026    0

instanceof / baseline ratios (best time, lower is better):
class-hit          1.3130x
interface-hit      1.3837x

using instanceof_fast_path_repro.php