Read entries of one phar from several coroutines

[EdmondDantes]

Closes #283.

Every compressed entry of an archive is decompressed into phar->ufp, one stream shared by every entry of that archive, at the offset the entry takes from it before it starts writing. Every call of that span parks — seek to the end, remember the offset, append the decompression filter, copy from the archive stream, flush, remove the filter — so two coroutines opening two compressed entries interleaved: the second appended its own filter to the same write chain and put its bytes at the offset the first had remembered. Four gzipped entries read by four coroutines answered internal corruption of phar "..." (actual filesize mismatch on file "...") for three of the four, on every run.

The engine side is php-src 353ccf7b070 (true-async, merged into true-async-stable). It holds the span as one unit: both sides of the archive stream around it and both sides of the uncompressed-file stream inside them, taken write-side first, the order php_stream_seek() and the rest of the stream layer take them. The archive stream is remembered once instead of read again after each park, and the entry is examined a second time under the lock, since another coroutine may have opened it while this one queued.

The call also holds an archive reference: phar_get_entry_data() takes its own only after phar_open_entry_fp() has returned, and without one the coroutine that finished first dropped the last reference and phar_archive_delref() closed the archive stream the others were queued on. The count is restored by hand — a teardown at zero closes the stream the caller is about to read — so a teardown due while the call was parked falls to whoever drops the count to zero next.

Reading one archive is serialized per archive as a result, stored entries included.

This PR carries the test and the changelog entry.

• tests/io/101-phar_entries_decompressed_at_once.phpt: three broken entries of four before the engine change, 10 green runs of 10 after.
• ext/phar/tests: 565 of 565.
• ext/async/tests plus php-src file, streams, filters, zlib and phar: 3221 tests, 3 failures, all three the local symlink artefacts (curl 063, curl 064, io 082).

Left open, found while reviewing this change and not caused by it: phar_open_entry_fp() does not hold the entry itself across a park, so phar_entry_remove() from another coroutine can free the phar_entry_info under it; and two coroutines can both open the archive stream, since phar_open_archive_fp() does not re-check after php_stream_open_wrapper() parks.

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