soroban-rpc: adapt to value overhaul changes

[2opremio]

What

Adapt soroban-rpc to the new value overhaul XDR changes (that is stellar/go#4814 , which in turn comes from stellar/stellar-xdr#70 )

Why

It's part of #471

It closes #477

Known limitations

TODO:

• fix integration tests (it requires bumping the core build)

[2opremio]

Related #516

@paulbellamy should I retarget the merge to the branch in the PR above?

[2opremio]

Integration tests are failing due to an OOM panic:

fatal error: runtime: out of memory

runtime stack:
runtime.throw({0x1c232d8?, 0x804000000?})
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/panic.go:1047 +0x5d fp=0x7fd75affdc20 sp=0x7fd75affdbf0 pc=0x5c8ddd
runtime.sysMapOS(0xc003400000, 0x800400000?)
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/mem_linux.go:187 +0x11b fp=0x7fd75affdc68 sp=0x7fd75affdc20 pc=0x5a9adb
runtime.sysMap(0x2e42180?, 0xc3ffffffff?, 0x2e52318?)
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/mem.go:142 +0x35 fp=0x7fd75affdc98 sp=0x7fd75affdc68 pc=0x5a94b5
runtime.(*mheap).grow(0x2e42180, 0x400002?)
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/mheap.go:1522 +0x245 fp=0x7fd75affdd10 sp=0x7fd75affdc98 pc=0x5b9c65
runtime.(*mheap).allocSpan(0x2e42180, 0x400002, 0x0, 0x0?)
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/mheap.go:1243 +0x1b7 fp=0x7fd75affdda8 sp=0x7fd75affdd10 pc=0x5b93b7
runtime.(*mheap).alloc.func1()
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/mheap.go:961 +0x65 fp=0x7fd75affddf0 sp=0x7fd75affdda8 pc=0x5b8e65
runtime.systemstack()
	/opt/hostedtoolcache/go/1.20.1/x64/src/runtime/asm_amd64.s:496 +0x49 fp=0x7fd75affddf8 sp=0x7fd75affddf0 pc=0x5feda9

[2opremio]

Now that I think about it, integration tests cannot succeed without #516 (since we need to update the test contracts).

However, we shouldn't be running out of memory.

[tsachiherman]

Looks all good to me.
It's unfortunate that these changes were needed, but I can think of any way would could have avoided these.