fix(sqlite3): use recursive mkdir when creating SQLite3 DB directory

mkdir() without the recursive flag fails if any intermediate directory
does not exist. Passing true as the third argument ensures the full path
is created, matching the behaviour expected on a fresh install.

fix(ezsession): PHP 8 — guard $GLOBALS['eZCurrentAccess'] before access

PHP 8 issues E_WARNING (treated as fatal by strict callers) when reading
an undefined global variable or accessing an array offset on null.
Use null-coalescing and isset() guard so session name generation skips
the md5 suffix when eZCurrentAccess is not yet populated (e.g. during
legacy autoload generation outside a full request context).

fix(ezsession): PHP 8 compat — read() returns '', gc() uses time() + gcStartTime

Bug1: read() returned false on DB-not-connected and no-row paths. PHP 8
  enforces SessionHandlerInterface strictly — false causes a recursive
  session restart ("Cannot call session save handler in a recursive manner").
  Fixed: both failure paths now return ''.

Bug2: gc() WHERE clause used $maxLifeTime (a duration, e.g. 1440 seconds)
  against expiration_time (an absolute Unix timestamp). The condition
  'expiration_time < 1440' never matched any real session, so expired
  sessions were never deleted. Fixed: both iterating and non-iterating
  paths now use time().

Bug3: gc() timeout guard computed elapsed time as ($stopTime - $maxLifeTime),
  treating $maxLifeTime as a start timestamp (~1.7 billion seconds elapsed),
  so the guard always fired after the first batch. Fixed: $gcStartTime =
  time() is captured before the do-while loop and used as the reference.

Tests: tests/tests/lib/ezsession/EzpSessionHandlerDBPhp8BugfixesTest.php
  12 tests, 28 assertions, PHPUnit 13.0.0 / PHP 8.5.5, zero notices,
  no live DB or eZ kernel required (hand-rolled stubs).

Docs: doc/bc/6.0/ezpsessionhandlerdb-php8-bugfix-and-tests.md

SQLite3: register eZSQLite3DB autoload + support absolute DB path

Two fixes to enable the legacy kernel to work with a shared Doctrine/DBAL
SQLite database file (as used by the Platform v4 new-stack integration):

autoload/ezp_kernel.php:
- Added 'eZSQLite3DB' => 'lib/ezdb/classes/ezsqlite3db.php' entry so PHP
  can autoload the class. Without this the [DatabaseSettings] ImplementationAlias
  sqlite3=eZSQLite3DB mapping in site.ini resulted in a fatal autoload failure
  and a null DB connection.

lib/ezdb/classes/ezsqlite3db.php:
- connect() now detects when $fileName is an absolute path (starts with /)
  and uses it directly instead of prepending 'var/storage/sqlite3/'. This
  allows the legacy bridge to pass the full absolute path from DBAL's
  SQLite connection params ('path' key) via site.ini DatabaseSettings/Database,
  so both stacks share the same .db file rather than each creating a separate one.

Added: Added rstring, ristring and many other php string operators as template operators. New features.

Updated: Upgraded phpunit test suite support to v13. Upgrade.

Revise issue tracker links and eZ Platform description

Updated issue tracker links and clarified eZ Platform information.