[Runtime] Honor the base argument in atoi_int32_base (#24677)

### Problem
`iree_string_view_atoi_int32_base` ignores its `base` argument.

### Root cause
`runtime/src/iree/base/string_view.c:387` calls `strtol(temp, &end, 0)`
— the `base` parameter is never used, so any requested radix is silently
discarded and the string is parsed with C auto-detection (leading `0x` →
hex, leading `0` → octal, else decimal). The three sibling `_base`
functions forward the argument correctly: `strtoul(temp, &end, base)`
(uint32, :413), `strtoll(..., base)` (int64, :436), `strtoull(...,
base)` (uint64, :462). The non-`base` wrapper
`iree_string_view_atoi_int32` already passes `0` explicitly (:399), so
the `_base` variant is clearly meant to honor a caller-supplied radix. A
caller requesting base 16 or 2 gets wrong values (e.g. base=16 `"10"` →
10 instead of 16).

### Fix
Forward `base` to `strtol`, matching the sibling `_base` functions.

### Verification
Static reasoning + sibling consistency; trivially checkable:
`strtol("10", &e, 16) == 16` vs the current `strtol("10", &e, 0) == 10`.
(No full runtime build on my machine — happy to add a unit test if
useful.)

Signed-off-by: Eylon Krause <eylon1909@gmail.com>