test(canton): cover template suffix matching near-misses

[Pessina]

Follow-up from PR #740.

Code:

mpc/chain-signatures/node/src/indexer_canton/ledger_api.rs

Lines 373 to 380 in 93c8e00

	/// Check if a template ID matches a given suffix at a module boundary.
	/// Requires the suffix to be preceded by `:` (package separator) or match exactly.
	///
	/// TODO(test): every event gets filtered through this — a bug means events are
	/// silently ignored. Test exact match ("Signer:Signer"), prefix match
	/// ("abc123:Signer:Signer"), and near-misses ("FakeSigner:Signer",
	/// "Signer:SignerExtra").
	pub fn template_suffix_matches(template_id: &str, suffix: &str) -> bool {

Context: every Canton event filter depends on template_suffix_matches. Add tests for exact match (Signer:Signer), package-prefixed match (abc123:Signer:Signer), and near-misses like FakeSigner:Signer and Signer:SignerExtra so malformed template IDs are not silently accepted or valid events ignored.