feat: Fully use protobuf, fix controller issues and cleanup (#305)

## Description
### First commit
Restructured protobuf schemas to make them easier to use across
languages, switched to using them in-place of JSON for signaling as
well, so there's no 2 different message formats flying about. Few new
message types to deal with clients and nestri-servers better (not final
format, may see changes still).

General cleanup of dead/unused code along some bug squashing and package
updates.

TODO for future commits:
- [x] Fix additional controllers not doing inputs (possibly needs
vimputti changes)
- [x] ~~Restructure relay protocols code a bit, to reduce bloatiness of
the currently single file for them, more code re-use.~~
- Gonna keep this PR somewhat manageable without poking more at relay..
- [x] ~~Try to fix issue where with multiple clients, static stream
content causes video to freeze until there's some movement.~~
- Was caused by server tuned profile being `throughput-performance`,
causing CPU latency to be too high.
- [x] Ponder the orb


### Second + third commit
Redid the controller polling handling and fixed multi-controller
handling in vimputti and nestri code sides. Remove some dead relay code
as well to clean up the protocol source file, we'll revisit the meshing
functionality later.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added software rendering option and MangoHud runtime config;
controller sessions now support reconnection and batched state updates
with persistent session IDs.

* **Bug Fixes**
* Restored previously-filtered NES-like gamepads so they connect
correctly.

* **Chores**
* Modernized dependencies and protobuf tooling, migrated to
protobuf-based messaging and streaming, and removed obsolete CUDA build
steps.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: DatCaptainHorse <DatCaptainHorse@users.noreply.github.com>

packages/relay/internal/common/ice_helper.go

@@ -0,0 +1,53 @@
+package common
+
+import (
+	"log/slog"
+
+	"github.com/pion/webrtc/v4"
+)
+
+// ICEHelper holds webrtc.ICECandidateInit(s) until remote candidate is set for given webrtc.PeerConnection
+// Held candidates should be flushed at the end of negotiation to ensure all are available for connection
+type ICEHelper struct {
+	candidates []webrtc.ICECandidateInit
+	pc         *webrtc.PeerConnection
+}
+
+func NewICEHelper(pc *webrtc.PeerConnection) *ICEHelper {
+	return &ICEHelper{
+		pc:         pc,
+		candidates: make([]webrtc.ICECandidateInit, 0),
+	}
+}
+
+func (ice *ICEHelper) SetPeerConnection(pc *webrtc.PeerConnection) {
+	ice.pc = pc
+}
+
+func (ice *ICEHelper) AddCandidate(c webrtc.ICECandidateInit) {
+	if ice.pc != nil {
+		if ice.pc.RemoteDescription() != nil {
+			// Add immediately if remote is set
+			if err := ice.pc.AddICECandidate(c); err != nil {
+				slog.Error("Failed to add ICE candidate", "err", err)
+			}
+			// Also flush held candidates automatically
+			ice.FlushHeldCandidates()
+		} else {
+			// Hold in slice until remote is set
+			ice.candidates = append(ice.candidates, c)
+		}
+	}
+}
+
+func (ice *ICEHelper) FlushHeldCandidates() {
+	if ice.pc != nil && len(ice.candidates) > 0 {
+		for _, heldCandidate := range ice.candidates {
+			if err := ice.pc.AddICECandidate(heldCandidate); err != nil {
+				slog.Error("Failed to add held ICE candidate", "err", err)
+			}
+		}
+		// Clear the held candidates
+		ice.candidates = make([]webrtc.ICECandidateInit, 0)
+	}
+}