proxy,ui-svelte: add request/response capturing (#508)

Add saving request and response headers and bodies that go through
llama-swap in memory.

- captureBuffer added to configuration. Captures are enabled by default.
- 5MB of memory is allocated for req/response captures in a ring buffer.
Setting captureBuffer to 0 will disable captures.
- UI elements to view captured data added to Activity page. Includes
some
QOL features like json formatting and recombining SSE chat streams
- capture saving is done at the byte level and has minimal impact on
llama-swap performance

Fixes #464 
Ref #503

proxy/config/config.go

@@ -123,6 +123,7 @@ type Config struct {
 	LogTimeFormat      string                 `yaml:"logTimeFormat"`
 	LogToStdout        string                 `yaml:"logToStdout"`
 	MetricsMaxInMemory int                    `yaml:"metricsMaxInMemory"`
+	CaptureBuffer      int                    `yaml:"captureBuffer"`
 	Models             map[string]ModelConfig `yaml:"models"` /* key is model ID */
 	Profiles           map[string][]string    `yaml:"profiles"`
 	Groups             map[string]GroupConfig `yaml:"groups"` /* key is group ID */
@@ -201,6 +202,7 @@ func LoadConfigFromReader(r io.Reader) (Config, error) {
 		LogTimeFormat:      "",
 		LogToStdout:        LogToStdoutProxy,
 		MetricsMaxInMemory: 1000,
+		CaptureBuffer:      5,
 	}
 	if err = yaml.Unmarshal([]byte(yamlStr), &config); err != nil {
 		return Config{}, err

proxy/config/config_posix_test.go

@@ -215,6 +215,7 @@ groups:
 		},
 		HealthCheckTimeout: 15,
 		MetricsMaxInMemory: 1000,
+		CaptureBuffer:      5,
 		Profiles: map[string][]string{
 			"test": {"model1", "model2"},
 		},

proxy/config/config_windows_test.go

@@ -204,6 +204,7 @@ groups:
 		},
 		HealthCheckTimeout: 15,
 		MetricsMaxInMemory: 1000,
+		CaptureBuffer:      5,
 		Profiles: map[string][]string{
 			"test": {"model1", "model2"},
 		},