fix(memstore): UintDefault rejected every positive int

[Qalipso]

UintDefault returns the default value and a not-found error for any plain int, on every 64-bit platform.

var p memstore.Store
p.Set("n", 8)
p.GetUintDefault("n", 0) // returns 0, not 8

Cause

var maxValue uint64 = math.MaxUint32
if x64 {
    maxValue = math.MaxUint64
}
...
case int:
    if vv < 0 || vv > int(maxValue) {
        return def, e.notFound(uintType)
    }

On a 64-bit platform maxValue is math.MaxUint64, so the conversion int(maxValue) wraps to -1. The guard becomes vv > -1, which is true for every positive int, so the value is rejected.

Fix

int and uint have the same width in Go, so math.MaxInt <= math.MaxUint always holds and every non-negative int is representable as a uint. Only the sign needs checking. The comparison against maxValue is removed from the int case; maxValue is still used by the uint64 case, which is correct as written (on 32-bit it properly rejects values above math.MaxUint32).

The sized getters (Uint8Default and friends) use literal bounds such as math.MaxUint8 and were never affected.

Verification

The three added tests fail on main and pass with the fix:

before:  --- FAIL: TestUintDefaultInt      expected 8 but got 0
         --- FAIL: TestUintDefaultMaxInt   not found: n as uint (uint)
after:   ok  github.com/kataras/iris/v12/core/memstore

TestUintDefaultNegativeInt passes both before and after, confirming the sign check is preserved. go vet, go test -race and gofmt are clean, ./core/... is green, and the package still builds and vets for GOARCH=386 and GOARCH=arm where uint is 32-bit.

---

Two notes:

1. This is independent of test(memstore): add tests for Store operations and Entry conversions #2607 (tests only, adds new files); the two do not touch the same lines and can merge in either order.

2. While confirming the sign behaviour I noticed the sized signed cases do not check the sign at all, so a negative value wraps silently rather than being rejected like the int case:

   int8(-1)  -> 18446744073709551615, err=nil
   int16(-1) -> 18446744073709551615, err=nil
   int32(-1) -> 18446744073709551615, err=nil
   int64(-1) -> 18446744073709551615, err=nil
   int(-1)   -> default, err=not found     <- correct
   

   I left that alone to keep this PR to one change. Happy to send it separately if you agree it should behave like the int case.

I did not open an issue first as the guidelines suggest — the diff is one line and the reproducer is above, but I'm glad to open one if you'd prefer.

[CLAassistant]

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