tests/functional/lang: Add tests for builtins.fromTOML overflow

This adds regression tests for fromTOML overflow/underflow behavior.
Previous versions of toml11 used to saturate, but this was never an
intended behavior (and Snix/Nix 2.3/toml11 >= 4.0 validate this).

(cherry picked from Lix [1,2])

[1]: 7ee442079d
[2]: 4de09b6b54

tests/functional/lang/eval-fail-fromTOML-overflow.err.exp

@@ -0,0 +1,13 @@
+error:
+       … while calling the 'fromTOML' builtin
+         at /pwd/lang/eval-fail-fromTOML-overflow.nix:1:1:
+            1| builtins.fromTOML ''attr = 9223372036854775808''
+             | ^
+            2|
+
+       error: while parsing TOML: [error] toml::parse_dec_integer: too large integer: current max digits = 2^63
+        --> fromTOML
+          |
+        1 | attr = 9223372036854775808
+          |                           ^-- must be < 2^63
+       

tests/functional/lang/eval-fail-fromTOML-overflow.nix

@@ -0,0 +1 @@
+builtins.fromTOML ''attr = 9223372036854775808''

tests/functional/lang/eval-fail-fromTOML-underflow.err.exp

@@ -0,0 +1,13 @@
+error:
+       … while calling the 'fromTOML' builtin
+         at /pwd/lang/eval-fail-fromTOML-underflow.nix:1:1:
+            1| builtins.fromTOML ''attr = -9223372036854775809''
+             | ^
+            2|
+
+       error: while parsing TOML: [error] toml::parse_dec_integer: too large integer: current max digits = 2^63
+        --> fromTOML
+          |
+        1 | attr = -9223372036854775809
+          |                            ^-- must be < 2^63
+       

tests/functional/lang/eval-fail-fromTOML-underflow.nix

@@ -0,0 +1 @@
+builtins.fromTOML ''attr = -9223372036854775809''