Fix npub mention bugs, fix slowness when parsing large posts

Switch the post parser to use the same code as the content parser. This
was causing many issues, including performance issues.

Changelog-Fixed: Fix lag when creating large posts
Changelog-Fixed: Fix npub mentions failing to parse in some cases
Changelog-Added: Add r tag when mentioning a url
Changelog-Removed: Remove old @ and & hex key mentions

damus-c/nostr_bech32.h

@@ -26,6 +26,7 @@ enum nostr_bech32_type {
     NOSTR_BECH32_NEVENT = 4,
     NOSTR_BECH32_NRELAY = 5,
     NOSTR_BECH32_NADDR = 6,
+    NOSTR_BECH32_NSEC = 7,
 };
 
 struct bech32_note {
@@ -36,6 +37,10 @@ struct bech32_npub {
     const u8 *pubkey;
 };
 
+struct bech32_nsec {
+    const u8 *nsec;
+};
+
 struct bech32_nevent {
     struct relays relays;
     const u8 *event_id;
@@ -65,6 +70,7 @@ typedef struct nostr_bech32 {
     union {
         struct bech32_note note;
         struct bech32_npub npub;
+        struct bech32_nsec nsec;
         struct bech32_nevent nevent;
         struct bech32_nprofile nprofile;
         struct bech32_naddr naddr;