fix(params): accept native integer types for numeric tool parameters

[harish-gaggar]

Summary

Accept native integer and json.Number values in shared numeric parameter coercion so MCP clients that send JSON integers (not only float64) can call issue tools successfully.

Why

Fixes #2807

Some MCP hosts pass issue_number as a JSON integer (int / json.Number). RequiredInt only accepted float64 and numeric strings, so valid calls failed before reaching the GitHub API.

What changed

• Extend toInt / toInt64 to handle native integer types and json.Number without float64 round-trip precision loss.
• Add unit tests in params_test.go and a regression case in issues_test.go for issue_read with int issue_number.

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Tool names and input schemas are unchanged; only argument parsing is more permissive for numeric fields.

Prompts tested (tool changes only)

N/A — no tool schema changes. Regression covered by unit/handler tests for issue_read with integer issue_number.

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR
• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with go test ./pkg/github -run 'Test_RequiredInt|Test_RequiredBigInt|Test_GetIssue' -count=1

Docs

• Not needed
• Updated (README / docs / examples)