Keep the oneoff payload within EveryPay's field limits and reword the statement text

[acirtautas]

Summary

• Billing/shipping address fields are capped at the character limits EveryPay enforces from 2026-10-01 (city/line1 50, postcode 16), using mb_substr so multibyte letters count as characters. A truncated address still feeds fraud scoring; an over-long one could reject the whole request.
• order_reference is transliterated and reduced to the charset the spec allows, with the order-number prefix capped at 100 characters (the Open Banking limit is 120). Sylius' default numeric order numbers pass untouched; the -{paymentId} suffix keeps the reference unique either way.
• The Open Banking statement text becomes {channel} ({number}) instead of {channel} order {number} - a language-neutral noun phrase that also reads naturally when the platform prefixes the refund transfer's copy of it with Refund - . The 65-character cap now trims the channel name, never the order number.

Companion to #9, which updates the distilled API reference these constraints come from.

Test plan

• vendor/bin/phpunit - 111 tests green
• vendor/bin/behat --strict - 15 scenarios green
• vendor/bin/phpstan analyse (level 9) and vendor/bin/ecs check - clean

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