Fix gocritic lint warnings

[JamieMagee]

Fixes the 8 gocritic warnings reported by golangci-lint.

What changed:

• ifElseChain: Converted 4 if-else chains to switch statements (in git_server_test.go, github_api_test.go, nuget_feed.go, oidc_credential.go)
• regexpMust: Moved a constant regexp pattern in python_index.go to a package-level regexp.MustCompile so it's compiled once instead of on every request
• assignOp: Used += instead of x = x + y in logging.go
• exitAfterDefer: Replaced log.Fatal calls in main.go with log.Println + return so deferred file.Close() actually runs on early exit

[Copilot]

Pull request overview

This PR addresses gocritic warnings flagged by golangci-lint across the proxy codebase, primarily by refactoring control flow, reducing repeated work, and adjusting error-exit behavior.

Changes:

• Replaced several if/else chains with switch statements.
• Precompiled a Python index URL regexp to avoid compiling it per request.
• Replaced some log.Fatal(...) exits with log.Println(...) + return to allow deferred cleanup to run.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
main.go	Replaces log.Fatal with log.Println + return in several failure paths.
internal/oidc/oidc_credential.go	Refactors OIDC parameter selection from if/else to switch.
internal/logging/logging.go	Uses += for string concatenation in cached-response logging.
internal/handlers/python_index.go	Moves regexp compilation to a package-level regexp.MustCompile.
internal/handlers/nuget_feed.go	Refactors response-type branching from if/else to switch.
internal/handlers/github_api_test.go	Converts an if/else chain to a switch in a table-driven test.
internal/handlers/git_server_test.go	Converts an if/else chain to a switch in a table-driven test.

Comments suppressed due to low confidence (1)

main.go:100

• With log.Println(err); return on ListenAndServe failure, proxy.Close() (which writes cache/metrics) is skipped. If the goal is to avoid log.Fatal while still running defers, consider defering proxy.Close() right after newProxy(...) so it runs on all exit paths.

	log.Printf("Listening (%s)", *addr)
	if err := server.ListenAndServe(); err != http.ErrServerClosed {
		log.Println(err)
		return
	}

	if err := proxy.Close(); err != nil {
		log.Println(err)
		return

[Copilot]

bodyString[:10] will panic when the response body is shorter than 10 bytes (including empty/whitespace-only bodies). Guard the slice with a length check (or log the whole string capped safely) before slicing.

Suggested change

	logging.RequestLogf(nil, "unknown API response: %s...", bodyString[:10])
	preview := bodyString
	if len(preview) > 10 {
	preview = preview[:10]
	}
	logging.RequestLogf(nil, "unknown API response: %s...", preview)

[Copilot]

rolleName is defined from cred.GetString("role-name"), but the AWS case still references roleName, which is undefined. This will fail to compile and also drops the role-name value. Rename rolleName back to roleName (or update the switch case and struct assignment to use the same identifier).

[Copilot]

These early returns from main() log the error but exit with status code 0. For a CLI/service this can make startup failures look like success to the caller/supervisor. Consider returning a non-zero exit code (e.g., track an exitCode and defer os.Exit(exitCode) so deferred file.Close() still runs).

This issue also appears on line 92 of the same file.