Parse event stream fields without a colon

[bensynapse]

I run Live Tennis API.

A bare id line currently leaves the previous event ID set. The next reconnect then sends that stale Last-Event-ID header.

The SSE parsing rules define an empty value for fields without a colon.

The fix clears bare id fields and preserves empty lines from bare data fields. A bare retry remains ignored.

The tests check parser output, decoder state and the reconnect request headers. Five regression cases fail against the original parser.

PHP 8.4: vendor/bin/phpunit --coverage-text --coverage-clover=clover.xml passes all 121 tests and 298 assertions. The workflow's coverage check passes with 100% statement coverage.

PHP 7.2: vendor/bin/phpunit -c phpunit.xml.legacy also passes all 121 tests and 298 assertions.

[bensynapse]

I fixed the PHP 5.6 failure in 80ba24b. Empty field values now stay strings, so event: keeps the default message type.
The existing regression reproduces the error before this fix. All 121 tests pass with 100% coverage on PHP 5.6 and PHP 8.4.

[clue]

@bensynapse Thanks for looking into this and fixing the legacy builds, changes LGTM! Matches the spec and a local spike I had for this back in 2022, so great to see this land with proper tests Keep it coming 👍