fix(session): handle special characters in search filters

[twio142]

The "contains" filter would previously fail when searching for a string containing a hyphen (e.g., "repo-name").

This is fixed by using a literal substring search, ignoring Lua pattern characters.

[moyiz]

Nice catch, thanks.
Please apply this patch to add a test case:

diff --git i/tests/session_spec.lua w/tests/session_spec.lua
index 26772c0..48646f0 100644
--- i/tests/session_spec.lua
+++ w/tests/session_spec.lua
@@ -16,6 +16,10 @@ local function gen_repos()
       foo = "gas",
       foo2 = "gas2",
     },
+    {
+      foo = "test-hyphen",
+      foo2 = "test-hyphen2",
+    },
   }
   for i, repo in ipairs(repos) do
     repo.repo_dir = i
@@ -37,6 +41,8 @@ local filters_to_nr = {
     },
     1,
   },
+
+  { { { name = "foo", value = "test-h", type = "contains" } }, 1 },
 }
 
 local function test_sanity()