feat: implement filter string parsing with Pest

Co-authored-by: aider (openai/andrew/openrouter/deepseek/deepseek-chat-v3.1) <aider@aider.chat>

src/filter.pest

@@ -0,0 +1,30 @@
+WHITESPACE = _{ " " | "\t" | "\n" | "\r" }
+
+filters = { filter ~ ("," ~ filters)? }
+filter = { filter_name ~ ("(" ~ options ~ ")")? }
+filter_name = @{ ASCII_ALPHA ~ (ASCII_ALPHANUMERIC | "_")* }
+
+options = { option ~ ("," ~ options)? }
+option = { (option_name ~ "=")? ~ option_value }
+option_name = @{ ASCII_ALPHA ~ (ASCII_ALPHANUMERIC | "_")* }
+
+option_value = { 
+    JSON_NUMBER |
+    JSON_STRING |
+    JSON_BOOLEAN
+}
+
+JSON_NUMBER = @{ 
+    ("-")? ~ 
+    ("0" | ASCII_NONZERO_DIGIT ~ ASCII_DIGIT*) ~ 
+    ("." ~ ASCII_DIGIT*)? ~ 
+    (("e" | "E") ~ ("+" | "-")? ~ ASCII_DIGIT+)? 
+}
+
+JSON_STRING = ${ 
+    "\"" ~ 
+    (("\\" ~ ANY) | (!("\"" | "\\") ~ ANY))* ~ 
+    "\"" 
+}
+
+JSON_BOOLEAN = ${ "true" | "false" }