Fix EmailTask undefined-method errors for serialized Message settings

[dereuromark]

Summary

Fixes #473.

Building on #472, this tackles pre-existing bugs in the same code path that were shadowed by the named-parameter crash. Once address settings stopped throwing first, the generic settings loop started calling undefined methods and re-hitting the named-param issue on non-address keys:

Error: Call to undefined method Cake\Mailer\Message::setAppCharset()
Error: Unknown named parameter $X-Custom  (headers map)

Fix

Before the generic settings loop, handle the mismatched/unsafe keys explicitly:

Settings key	Action
htmlMessage	Message::setBodyHtml()
textMessage	Message::setBodyText()
appCharset	Message::setCharset() when no explicit charset is also provided (appCharset has no dedicated setter anywhere)
readReceipt	added to the address-setter list so associative email => name inputs work without PHP 8 named-parameter issues
headers	Message::setHeaders() called with the map as a single positional argument, so string header names are not interpreted as named parameters

The generic call_user_func_array fallback is kept, so any custom set* keys consumers currently rely on continue to work unchanged.

Covered all 20 entries in Message::$serializableProperties:

• 8 address-shape keys (to/from/cc/bcc/replyTo/sender/returnPath/readReceipt) — routed through the address path from Fix EmailTask named-parameter error for associative address arrays #472
• 3 keys without matching setters (htmlMessage/textMessage/appCharset) — routed to their real Message methods
• 1 key with an associative-value named-param risk (headers) — routed as a single positional argument
• 8 straightforward scalar keys (subject/emailFormat/emailPattern/domain/messageId/charset/headerCharset/attachments) — continue via the existing generic/special-case paths (verified safe: non-associative values, no named-param risk)

Regression tests cover a payload that mirrors Message::__serialize() output and a settings-level associative headers map.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 77.22%. Comparing base (6eda87a) to head (5e29c24).

Files with missing lines	Patch %	Lines
src/Queue/Task/EmailTask.php	93.33%	1 Missing ⚠️
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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #474      +/-   ##
============================================
+ Coverage     77.15%   77.22%   +0.06%     
- Complexity      944      949       +5     
============================================
  Files            45       45              
  Lines          3182     3196      +14     
============================================
+ Hits           2455     2468      +13     
- Misses          727      728       +1     

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