Allow uppercase bech32 HRP

[tnull]

Previously, we would fail parsing Offers if the HRP didn't match our expected (lowercase) HRP. Here, we relax this check in accordance with the spec to also allow all-uppercase HRPs.

Discovered while upgrading LDK Node to 0.1.0-beta1, as we failed to parse uppercase offers (which used to work).

Related: rust-bitcoin/rust-bech32#208

[optout21]

Some tests would be useful, to make behavior more explicit (lowercase/uppercase/mixedcase).

[optout21]

Note: doesn't help much, but might be related to / caused by #3270

[tnull]

Some tests would be useful, to make behavior more explicit (lowercase/uppercase/mixedcase).

Yup, already on it, will push in a sec :)

[tnull]

Now pushed some test coverage.

[jkczyz]

LGTM. Please squash.

[tnull]

LGTM. Please squash.

Squashed and included the following minor changes to align exactly with the BOLT12 test vectors:

> git diff-tree -U2 afc9a5674 b8dabf51c
diff --git a/lightning/src/offers/parse.rs b/lightning/src/offers/parse.rs
index afd79b2a8..f3c481a9f 100644
--- a/lightning/src/offers/parse.rs
+++ b/lightning/src/offers/parse.rs
@@ -252,6 +252,6 @@ mod bolt12_tests {
                        "lno1pqps7sjqpgtyzm3qv4uxzmtsd3jjqer9wd3hy6tsw35k7msjzfpy7nz5yqcnygrfdej82um5wf5k2uckyypwa3eyt44h6txtxquqh7lz5djge4afgfjn7k4rgrkuag0jsd5xvxg",

-                       // An all-uppercase string is valid
-                       &"lno1pqps7sjqpgtyzm3qv4uxzmtsd3jjqer9wd3hy6tsw35k7msjzfpy7nz5yqcnygrfdej82um5wf5k2uckyypwa3eyt44h6txtxquqh7lz5djge4afgfjn7k4rgrkuag0jsd5xvxg".to_uppercase(),
+                       // Uppercase is valid
+                       "LNO1PQPS7SJQPGTYZM3QV4UXZMTSD3JJQER9WD3HY6TSW35K7MSJZFPY7NZ5YQCNYGRFDEJ82UM5WF5K2UCKYYPWA3EYT44H6TXTXQUQH7LZ5DJGE4AFGFJN7K4RGRKUAG0JSD5XVXG",

                        // + can join anywhere
@@ -292,5 +292,5 @@ mod bolt12_tests {
        fn fails_parsing_bech32_encoded_offers_with_mixed_casing() {
                // We assert that mixed-case encoding fails to parse.
-               let mixed_case_offer = "lno1pqpS7sjqpgtyzm3qv4uxzmtsd3jjqer9wd3hy6tsw35k7msjzfpy7nz5yqcnygrfdej82um5wf5k2uckyypwa3eyt44h6txtxquqh7lz5djge4afgfjn7k4rgrkuag0jsd5xvxg";
+               let mixed_case_offer = "LnO1PqPs7sJqPgTyZm3qV4UxZmTsD3JjQeR9Wd3hY6TsW35k7mSjZfPy7nZ5YqCnYgRfDeJ82uM5Wf5k2uCkYyPwA3EyT44h6tXtXqUqH7Lz5dJgE4AfGfJn7k4rGrKuAg0jSd5xVxG";
                match mixed_case_offer.parse::<Offer>() {
                        Ok(_) => panic!("Valid offer: {}", mixed_case_offer),

[tnull]

Rebased on 0.1 as Github wanted me to.

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.32%. Comparing base (afa2f9c) to head (7272969).
Report is 3 commits behind head on 0.1.

Files with missing lines	Patch %	Lines
lightning/src/offers/parse.rs	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              0.1    #3505      +/-   ##
==========================================
+ Coverage   88.26%   88.32%   +0.05%     
==========================================
  Files         149      149              
  Lines      112915   112926      +11     
  Branches   112915   112926      +11     
==========================================
+ Hits        99666    99740      +74     
+ Misses      10754    10697      -57     
+ Partials     2495     2489       -6     

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