tree-sitter-go: revert fork to crates.io once upstream #198 lands #8

Debt

Cargo.toml pins tree-sitter-go to a fork instead of crates.io:

tree-sitter-go = { git = "https://github.com/O6lvl4/tree-sitter-go", rev = "33f5f52" }

The fork (go-1.27-generic-methods) adds type_parameters to method_declaration so Go 1.27 generic methods parse. Introduced in #6; without it, files using generic methods are ~86% unparsed and land in the unanalyzed bucket from #4.

The fork is equivalent to upstream tree-sitter/tree-sitter-go#198 (2 lines in grammar.js + regenerated artifacts).

When this is actionable

Both must be true:

1. Upstream #198 is merged, and
2. A new tree-sitter-go release is cut on crates.io that includes it (i.e. a version > 0.25.0 whose grammar has the method_declaration type_parameters field).

As of 2026-08-30, #198 is open (mergeable) and the latest crates.io release is 0.25.0 (no generic-method support). So this cannot be done yet — reverting now would send types.go back to unanalyzed.

Quick check for when it's ready:

# does the newest published tree-sitter-go parse a generic method?
curl -s https://crates.io/api/v1/crates/tree-sitter-go | jq -r '.crate.max_version'

Revert steps

1. Bump Cargo.toml: tree-sitter-go = "<new version>" (drop the git pin + the fork comment).
2. cargo update -p tree-sitter-go && cargo build.
3. Confirm the regression test still passes: cargo test --test e2e_languages e2e_go_generic_method_parses.
4. Confirm a project with go.mod below 1.27 still gets go-generic-method (the src/version.rs gate from 宣言バージョンより新しい構文を検出する (go vet stdversion 相当) #7 is independent of the grammar source).
5. Archive/delete the O6lvl4/tree-sitter-go fork branch.

Optional

Nudge upstream #198 with the real-world evidence (a public project where the 2-line change recovers 85.6% of a file from unparseable) to help it merge.