[libc][NFCI] Remove lane size template argument on RPC server (#84557)

Summary:
We previously changed the data layout for the RPC buffer to make it lane
size agnostic. I put off changing the size for the server case to make
the patch smaller. This patch simply reorganizes code by making the lane
size an argument to the port rather than a templtae size. Heavily
simplifies a lot of code, no more `std::variant`.

Author: jhuber6

libc/src/__support/RPC/rpc.h

@@ -310,7 +310,7 @@ template <bool T> struct Port {
   LIBC_INLINE Port &operator=(Port &&) = default;
 
   friend struct Client;
-  template <uint32_t U> friend struct Server;
+  friend struct Server;
   friend class cpp::optional<Port<T>>;
 
 public:
@@ -369,7 +369,7 @@ static_assert(cpp::is_trivially_copyable<Client>::value &&
               "The client is not trivially copyable from the server");
 
 /// The RPC server used to respond to the client.
-template <uint32_t lane_size> struct Server {
+struct Server {
   LIBC_INLINE Server() = default;
   LIBC_INLINE Server(const Server &) = delete;
   LIBC_INLINE Server &operator=(const Server &) = delete;
@@ -379,10 +379,12 @@ template <uint32_t lane_size> struct Server {
       : process(port_count, buffer) {}
 
   using Port = rpc::Port<true>;
-  LIBC_INLINE cpp::optional<Port> try_open(uint32_t start = 0);
-  LIBC_INLINE Port open();
+  LIBC_INLINE cpp::optional<Port> try_open(uint32_t lane_size,
+                                           uint32_t start = 0);
+  LIBC_INLINE Port open(uint32_t lane_size);
 
-  LIBC_INLINE static uint64_t allocation_size(uint32_t port_count) {
+  LIBC_INLINE static uint64_t allocation_size(uint32_t lane_size,
+                                              uint32_t port_count) {
     return Process<true>::allocation_size(port_count, lane_size);
   }
 
@@ -556,10 +558,8 @@ template <uint16_t opcode>
 
 /// Attempts to open a port to use as the server. The server can only open a
 /// port if it has a pending receive operation
-template <uint32_t lane_size>
-[[clang::convergent]] LIBC_INLINE
-    cpp::optional<typename Server<lane_size>::Port>
-    Server<lane_size>::try_open(uint32_t start) {
+[[clang::convergent]] LIBC_INLINE cpp::optional<typename Server::Port>
+Server::try_open(uint32_t lane_size, uint32_t start) {
   // Perform a naive linear scan for a port that has a pending request.
   for (uint32_t index = start; index < process.port_count; ++index) {
     uint64_t lane_mask = gpu::get_lane_mask();
@@ -588,10 +588,9 @@ template <uint32_t lane_size>
   return cpp::nullopt;
 }
 
-template <uint32_t lane_size>
-LIBC_INLINE typename Server<lane_size>::Port Server<lane_size>::open() {
+LIBC_INLINE Server::Port Server::open(uint32_t lane_size) {
   for (;;) {
-    if (cpp::optional<Server::Port> p = try_open())
+    if (cpp::optional<Server::Port> p = try_open(lane_size))
       return cpp::move(p.value());
     sleep_briefly();
   }