cli: improve error messages in generated Rust test template (ANCHOR_WALLET, program id)

[yukikm]

Same behavior, clearer failures: the generated Rust unit test template now uses actionable messages instead of bare unwrap()s (missing $ANCHOR_WALLET, invalid program id string, failing to load program client, failing to send tx).

[vercel]

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[Copilot]

Pull request overview

This PR improves error handling in the generated Rust unit test template by replacing bare unwrap() calls with more descriptive error messages using expect() and unwrap_or_else(). The changes help developers quickly identify and fix issues related to missing or invalid environment variables, program IDs, and transaction failures.

Changes:

• Replaced unwrap() with expect() for ANCHOR_WALLET environment variable lookup with clear guidance message
• Added descriptive panic messages for keypair file reading, program ID parsing, program client loading, and transaction sending failures
• Changed Pubkey::try_from() to Pubkey::from_str() (both are valid, from_str is more idiomatic with the FromStr trait import)

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[Copilot]

The error message uses $ANCHOR_WALLET which is shell syntax for referencing an environment variable, but in this context, it's confusing since the actual path is already being displayed via the {anchor_wallet} interpolation. Consider removing the $ prefix and just say "Failed to read keypair at ANCHOR_WALLET" or "Failed to read keypair from ANCHOR_WALLET" to make it clearer that ANCHOR_WALLET is the environment variable name, not a shell expansion.

Suggested change

	panic!("Failed to read keypair at $ANCHOR_WALLET ({anchor_wallet}): {e}")
	panic!("Failed to read keypair at ANCHOR_WALLET ({anchor_wallet}): {e}")

[jamie-osec]

Duplicate of #4243