fix: use /v2 module path so v2 is consumable as a Go module (#39)

[wudidapaopao]

Problem

Fixes #39.

The v2.0.0 tag can't be consumed by the Go toolchain because its go.mod module path lacks the required major-version suffix:

$ go get github.com/chdb-io/chdb-go/v2@v2.0.0
go: ...: invalid version: go.mod has non-.../v2 module path "github.com/chdb-io/chdb-go" ...

Go's semantic import versioning requires that modules tagged v2.0.0+ declare the major version in the module path (github.com/chdb-io/chdb-go/v2). Since v0/v1 share the unsuffixed path, this never came up before the v2 bump.

Changes

• go.mod: module github.com/chdb-io/chdb-go → module github.com/chdb-io/chdb-go/v2
• Rewrote all internal imports of .../chdb and .../chdb-purego to the /v2 path
• Updated import examples in README.md, chdb.md, chdb/doc.md, lowApi.md
• Updated the go install github.com/chdb-io/chdb-go/v2@latest instruction
• Left genuine GitHub URLs (/issues/, /blob/, /actions/) untouched

Verification

go build ./...   # OK
go vet ./...      # OK
go build -o chdb-go .   # CLI OK

Follow-up (maintainer action)

This corrects the source, but the broken v2.0.0 tag remains. After merging, please cut a new patch tag so consumers can depend on it:

git tag v2.0.1 && git push origin v2.0.1

Then go get github.com/chdb-io/chdb-go/v2@v2.0.1 will work.

Note

Update module path to github.com/chdb-io/chdb-go/v2 for Go semantic import versioning

Updates go.mod module declaration and all internal import paths across the repository to use the /v2 suffix, making the v2 release consumable as a proper Go module. Documentation and example snippets in README and API docs are also updated to reflect the new import paths.

^{Macroscope summarized 7ad721c.}

[wudidapaopao]

@chibugai, review this PR.