Fix reactive getEx() ignoring PERSIST/KEEPTTL/EXAT/PXAT (fixes #7308) - #7309

What

Fixes getEx() in all 10 RedissonReactiveStringCommands.java module variants (Spring Data Redis 2.6 through 4.1) to check Expiration.isPersistent() / isKeepTtl() / isUnixTimestamp() and translate to the matching GETEX option, instead of always sending the raw expiration value as PX.

Why

See #7308 for the full writeup. Short version: Expiration encodes PERSIST/KEEPTTL as negative sentinel values internally. The current code sends whatever getExpirationTimeInMilliseconds() returns as a literal PX argument regardless of what was requested, so:

• Expiration.persistent() → GETEX key PX -1000 → Redis rejects it: ERR invalid expire time in 'getex' command
• Expiration.keepTtl() → GETEX key PX -2000 → same error
• Expiration.unixTimestamp(...) (EXAT/PXAT) → the absolute epoch value is sent as if it were a relative millisecond delay, landing decades in the future instead of at the intended time

This exact bug was already fixed on the sync side (RedissonConnection.getEx()) in commit 6c393a51f. This PR applies the identical fix to the reactive counterpart in the same files, which that commit didn't touch.

Changes

• getEx() in RedissonReactiveStringCommands.java, all 10 module variants that contain this method (redisson-spring-data-{26,27,30,31,32,33,34,35,40,41}):

if (expiration.isPersistent()) {
    m = write(keyBuf, ByteArrayCodec.INSTANCE, GETEX, keyBuf, "PERSIST");
} else if (expiration.isKeepTtl()) {
    m = write(keyBuf, ByteArrayCodec.INSTANCE, GETEX, keyBuf);
} else if (expiration.isUnixTimestamp()) {
    m = write(keyBuf, ByteArrayCodec.INSTANCE, GETEX, keyBuf,
            "PXAT", expiration.getExpirationTimeInMilliseconds());
} else {
    m = write(keyBuf, ByteArrayCodec.INSTANCE, GETEX, keyBuf,
            "PX", expiration.getExpirationTimeInMilliseconds());
}

Mirrors the sync fix's logic and option choices exactly (including always using PXAT with millisecond precision for the absolute-timestamp case, rather than branching between EXAT/PXAT by original unit).

• New test RedissonReactiveStringCommandsTest, added to all 10 module variants, covering all four Expiration variants (relative milliseconds, PERSIST, KEEPTTL, EXAT) against a real Redis instance.

Test plan

Before the fix, against both master and the latest release redisson-4.7.0:

testGetExRelativeMillis                      -> PASS (already worked)
testGetExPersistRemovesTtl                   -> ERROR: RedisSystem ERR invalid expire time in 'getex' command. params: [key, PX, -1000]
testGetExKeepTtlPreservesOriginalTtl         -> ERROR: RedisSystem ERR invalid expire time in 'getex' command. params: [key, PX, -2000]
testGetExAbsoluteSecondsUsesExatSemantics    -> FAIL: expected PTTL ~120000ms, got 1787146328998ms (~56.6 years)

After the fix, all four pass in every module (Tests run: 4, Failures: 0, Errors: 0, Skipped: 0 each).

Backward compatibility

No API or behavior change for the one case that already worked (plain relative expiration). PERSIST/KEEPTTL/EXAT/PXAT go from "throws" or "silently wrong" to "correct", which can only fix previously-broken behavior, not change any working behavior.