NQuadsSerializer: fix graphs handling

Merge pull request #13 from sweetrdf/feature/introduce-sweetrdf-json-ld

Replace ml/json-ld with sweetrdf/json-ld

Merge pull request #12 from sweetrdf/feature/php8.5

PHP 8.5 support

CreateBlankNodeTrait: generate blank node identifiers conformant with…

… the n-triple syntax

The n-triples syntax doesn't allow UCHARs (escapes in a form of a
\u{character code in hex}) in blank node identifiers, therefore a global
map from `{source's baseURI}/{blank node identifier in source}` to a
global sequential blank node identifier was implemented.

As a consequence a few tests have to be adjusted.

.github/workflows/test.yml: run phpstan on PHP 8.4

Files missing from the previous commit added

ResourceWrapper::read() and getContents(): strict check stream_get_co…

…ntents() return type

Merge pull request #9 from sweetrdf/issue7

Issue7

Merge pull request #6 from sweetrdf/feature/util-allow-rdfxml

Extend Util.php to accept rdfxml in getParser and getSerializer

TriGParser: fix stupid bugs and add missing test file