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Stephan Renatus 9c83b9948a wasm: replace wasmtime-go with wazero (#8815 )

The change replaces bytecodealliance/wasmtime-go/v44 (CGo) with
tetratelabs/wazero (pure Go)

- CGo eliminated — wazero is pure Go, so the whole internal/wasm/sdk
runtime no longer needs a C toolchain/cross-compilation story.
- The "env glue module" trick (glue.go) is the right solution to
wazero's constraint that a HostModuleBuilder can't export memory.
- Process-wide CompilationCache (sync.OnceValue): each unique policy is
compiled once per process, and discarded/re-instantiated VMs are cheap.
- Simplification in vm.go — dropping the ~25 closure fields (evalOneOff,
eval, heapPtrGet, …) in favor of mod.ExportedFunction(name) + a generic
call/callVoid/callOrCancel
- All tests pass (incl. internal/wasm/sdk/internal/wasm,
internal/wasm/sdk/opa). evalCompat for ABI 1.1 is retained.


----------

```
                                │ bf2bb5261c  │             13d2710058             │
                                │    sec/op    │   sec/op     vs base                │
WASMColdStartTargets/topdown-16    112.8µ ± 1%   113.3µ ± 1%        ~ (p=0.512 n=15)
WASMColdStartTargets/wasm-16      10.850m ± 1%   2.906m ± 1%  -73.22% (p=0.000 n=15)
geomean                            1.107m        573.9µ       -48.14%

benchmark \ host                local:tags=opa_wasm
                                            vs base
WASMColdStartTargets/topdown                      ~
WASMColdStartTargets/wasm                   -73.22%

```
```

            │ bf2bb5261c │             13d2710058             │
            │   sec/op    │   sec/op     vs base                │
WasmRego-16   4.976µ ± 1%   3.546µ ± 3%  -28.74% (p=0.000 n=15)

            │ bf2bb5261c  │              13d2710058               │
            │     B/op     │     B/op       vs base                 │
WasmRego-16   2.276Ki ± 0%   13.260Ki ± 0%  +482.50% (p=0.000 n=15)

            │ bf2bb5261c │            13d2710058             │
            │  allocs/op  │ allocs/op   vs base                │
WasmRego-16    46.00 ± 0%   33.00 ± 0%  -28.26% (p=0.000 n=15)

benchmark \ host    local:tags=opa_wasm
                                vs base
WasmRego                        -28.74%
```

> [!NOTE]
> When running benchmarks here, be aware that the memory previously used
was invisible to the benchmark machinery -- it was on the other side of
the CGo divide 🙈

Fixes #7557.

---------

Signed-off-by: Stephan Renatus <stephan.renatus@gmail.com>