[Fix] various todos about corner cases

[aMOPel]

• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L584
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L943
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L950
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L1128
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L1137
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L1181
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L1318
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L1330
• [ ] https://github.com/aMOPel/tree-sitter-nim/blob/main/grammar.js#L1448